The AM Forum

Hello Homebrew Buffs,

Well, since my 24 pill class-E rig blew up last week, (Rico Suave) I decided to go back to tubes...had been freezing in the shack this winter.  I've had great luck with 4X1's in the past and miss them dearly.   The old Fabio 4X1 rig was torn down to make room for the new class A linear amp system last year.  The class A linear is FB on SSB, but makes just too much heat and blower noise for AM use. I also wanted to make some big changes and improvements on Fabio I anyway, so here is the all-new FABIO II under construction!

Not much to see yet, but here are the finished and painted aluminum front panels. They are 19" wide and 26"/ 28" tall. They will front a 4-1000A  plate modulated by a pair.  Notice the tube viewing holes at the bottom.  The modulator panel is on the left and the RF final panel is on the right. I'm not particularly fond of drilling and blasting, so glad to have this stage finished.  The two chassis layouts are almost finished too.

The class C RF final will be neutralized, use a very large bandswitch, vacuum variables with counters, quiet squirrel cage blowers with Variacs and full metering.  (HV, plate current, screen current, grid current and fils)

There will be just one audio transformer - the modulation xfmr, to minimize phase shift. The modulators will be driven by a solid state MOSFET audio driver with heavy negative feedback from the moulation transformer secondary back to the 1 volt low level stage.  A broadcast RCA 1 KW modulation transformer with 75H of Heising reactor inductance will be employed.  The modulators will be run as grid-driven AB1 stages, (with 1000V  screen voltage) for maximum cleanliness.

There is a 4-step relay sequencer used to key each stage in a controlled manner - to reduce arcing tendencies.

The satin-white panels will have black lettering to match other rigs in the shack.

I should have the parts mounted in a day or so and will post some more pics. I expect first light testing in about 2 weeks.

The HV power supply is already built - it's the common supply in the shack giving 2, 3  or 4KV.  The solid state driver (designed by Frank/ GFZ) is from the original Fabio I - and the screen and grid supplies are recycled, as well as the sequencer.  So, it's mainly the RF  and modulator decks that are being built from scratch and will be much improved.  No more plexiglass except for the viewing windows.

More later.

T  

I'll never forgive you for injecting the Rico Suave video into my brain!

Viva Fabio II!

That looks ambitious, Tom!! If and when I get the 4-1000 I have igoing in an amp, I will use 4-400's to modulate it.Looking forward to more pictures as it takes shape!!

Is this a typo about the *1* kw broadcast mod iron  ;D

Yep, wish I had something bigger to handle the voltage, but this is all I have right now.  I will have to limit the HV to about 3-3.5 KV max.  It's the same xfmr I ran with Fabio I for a few years.

The RCA  mod transformer tag says:  1KVA,   pri = 10,500 ,  sec =  4300      (2.3 : 1   step down imp ratio)  
  
It weighs 144 pounds.  Applying the Tron rule of  10 lbs per 100 watts, this is about 1444 watts audio capacity.  No DC on the secondary.

T

I'll be following this project closely.  Waiting to hear you back on the air.

GL, Al

Tom,

Nice looking panels.  I'm a black wrinkle junkie myself.

What paint did you use on the panels and what do you use to cut the meter holes??

Fred

Izzat an easter egg in the grass?

Fred,

The sheet for the panels was found at the recycling metal scrap yard... I pay $1 per pound for aluminum sheet. Such a bargain.  I plan to make my own IBM-blue cabinets too.

I use a standard 2.5" hole saw for the meter holes that can be bought at any Ace hardware. Once we buy the drill bit assembly, the various saw sizes are cheap.   I used to use Greenlee punches, but I like these better.

I use standard enamel spray paint from Ace. Then put the panel next to the coal stove for a day to bake it. Works FB.


You may like the parts mounting and layout I am using. There are some unique ways I am supporting the vac variables as well as use of the front panel for supporting RF components.  Also, a shelving platform to support a second level.    Compact and easy servicing is the goal. Pics later.


Steve, that is one of the dormant vegetable gardens in the background. We dump some of the food scraps there, thus the Easter egg shells... ;D

T

This is a seriously ominous project. Is there a schematic handy anywhere besides a few squares of "bathroom tissue".

:)

FEEELEEP

Thanks a lot. I had forgotten it.

Too bad about the blowup after all that engineering.

The schematic basically follows this 813s X 813s  rig, except for using 4X1's, and the modulator screens are tied to a regulated 1000V:
 
http://www.amwindow.org/tech/htm/813/813.htm


Also, I am using a solid state audio driver as shown here:


http://amfone.net/Amforum/index.php?topic=23632.0



I have made some good progress and mounted a lot of parts, so should have a few 4X1 pictures to post in the next day or so...

T

The 4X1 RF deck has been assembled and ready for wiring.   I decided to make it two tubes in the final.  This will allow better matching to my existing 2:1 step down mod transformer as well as work better with the limited 3KV I have to limit the mod transformer to.   I can always pull out one tube and put in an air plug. It will run FB either way and is now more versatile.

Check out the method I use to mount the vacuum variables to the front panel. Easy and works great.

The rig is designed for easy servicing, as every component, including the tube chassis' can be removed easily.  The bandswitch is very large-spaced, allowing for any voltage I can apply.

I'll take some more complete pics once wiring has progressed and the panels get knobs and lettering.

T

RF DECK:

MODULATOR DECK  pics 1 & 2:


RF Deck Pic 3:

YOU are the TOMSTEIN of Amateur Radio!
I guess later we'll see the huge insulators in your shack with 10kv sparks jumping between them, like in the Frankenstein movies??

The tubes always are a pleasure to work with.

Fred

As usual on your creations Tom, fantastic job!  I can't wait to work you on the air with the beast! 

I also like the layout and it should fire up without incident. 

Most of all, enjoy the fun of the build. 

Joe, GMS

Actually that RF layout is potentially scary. How do you propose to keep that ancient glass vacuum variable from melting down? Even a ceramic one would be affected.

Carl

Thanks for the comments, guys.  It's coming along... wiring up the RF deck with copper flashing right now.

Carl:  You make a good point about exit tube exhaust onto the C1 vacuum variable.  I did consider this.  I monitor all of my tube exit temperatures with a dedicated digital temp readout for each rig. From experience,  I've found that when running a 4X1 ultra-conservatively in class C, the exit air 2" away usually will not get above 95 to 110F degrees. Using two tubes that are balancing the load, it should be less.  This temp should not hurt anything.

However, there is also the issue of constant thermal expansion and contraction that is probably not good. Even though a tube can take it easily, maybe the vac cap is more vulnerable to seal failure.  I may add an insulated shield bolted to the C1 bracket that deflects heat away from the vac variable to act as a heat shield. This will have an air gap barrier and act just like a wood burning stove shield.

** In fact, a fiberglass shield will give me a place to mount the plate coupling cap and leads to the plate caps at the same time!   I was wondering how I wud do that.

It was not an easy task to get the four tank components grouped closely together for RF stability, thus the close proximitry of the tube.  (bandswitch, C1, C2, L1)

Thanks for the heads up.

T

Well Tom, I wasnt considering "conservative" operation ;D

You coming to Nearfest?

You could have another fan in the RF cabinet somewhere cooling the capacitor and other components... and the deflector idea is also a good one.

Carl - Hope to make Deerfield at least for Friday.  Hope to catch ya at the dinner.

Steve, I opted to use the fiberglass deflector and it doubles to support the plate coupling cap.  

In the pics, the chassis is missing the filament transformer and screen/ grid power supplies. The platform will be all filled up once completed.  Notice the little shelf I added. Both the RF deck and mod decks have them for extra space. I am already using them for odds and ends.

Notice the bandswitch uses doubled up contacts and the leads are pretty short. The high power RF stuff is all wired.

The plate RF choke is home-wound and plenty enough to cover 160M.  BTW, the rig is presently designed to cover 40M -160M.  

Question:  I usually use parasitic suppressors in the plate. I have seen some guys get away without them.  Do you think the way the plate is connnected now will work or do I need to use separate balanced feeds for each tube and two suppressors?

T

More general shots:

I would make 2 changes in the RF amplifier layout

1) Use parasitic suppressors.  You are begging for trouble if you don't.  Heck, it's only being used up to 40 meters anyway.

2) If if were me, I would run individual, EQUAL length lines from the DC blocking capacitor to the plates of each of the tubes (might as well put the parasitic suppressors in while you're at it). 

-  Or run a shorter line to each tube (with individual parasitic suppressors), join them together and then run a single line from the joining point back to the DC blocking cap.  No matter how you do it, it is always better to by symmetrical all the way around.

Otherwise, looks good.

I like the TV tray, scissors jack relay server tray.  Very unique way to serve a quick "bite" or E-Snack between on/off states.   ;D

Thanks, Steve.

I added the symmetrical suppressors as described above.   Sometimes I KNOW I shud do it, but often get lazy and pay the price later on... :-)

Hopefully the layout for 160 - 40M is good enuff so I won't have to add in any suppressors to the grids.
It is grid driven with a link input and only 20K of swamping, so it will be very easy to drive, like under 15 watts or so.

T

Where did you get your 4-1000s?

Philip

Hi Philip,

Yes, 4X1's are rather scarce these days compared to yesteryear.   There was a time 20 years ago we could get them easily for $20 - $50 each at the flea markets. The BC and commercial rigs used them, but not anymore. So the supply has dried up.

I would put out "wanted" ads on the various QTH.com, etc boards and you will get replies. There are many older hams who have hoarded them thinking they wud build an amp someday, but never did.

The CB QRO and audiophile guys never embraced the tube, so there should be many out there.

Axe the seller to put a piece of white paper behind the tube and report if there are any "coffee stains" on the glass.  This is a good indication of hours on the tube. Also axe about plate deformaties or glass heat dimples.

 Be sure to use the black, plasdick socket for RF use. And a chimney is important to get air up and around the plate cap.

They are a great tube and will take a lot of abuse - as long as air is run by all the seals.  A chimney and good air flow will see to that.

T


** Update:  The 4X1 RF deck is almost all wired and I will post some pics soon.  I'm awaiting a robust vacuum relay for the antenna switching.     Next, the modulator deck.

 Be sure to use the black, plasdick socket for RF use. And a chimney is important to get air up and around the plate cap.
T
[/quote]

Hi Tom,
I have some of the Eimac cast sockets designed for forced air cooling.  I forget the Eimac part number but they are very heavy duty and have the opening for a hose connection to handle the cooling.  Have you found any problem when using them?
Joe, GMS

Hi Joe,

I have used them both for RF service up to 10M with no problems.  If we look at the alum ones, the lead length is not much different than the plastic sockets.

But I have been warned by some to stay wid the plastic sockets for RF and leave the aluminum ones for audio modulators.

Another thing is cooling.  I like the more direct path for air and ability to drill additional holes around the socket when using the plastic version.  Though, I have drilled holes in the alum sockets for more air too.

T



 

Thanks Tom.  Yep, I think I have a pair of the cast ones and it would be no problem putting those in modulator service.  So when I look for the RF side, I can go with the less expensive ones. 

My scheme is to use one high panel similar to yours but to put a steel Bud shelf above the tubes with ample spacing so air can escape and then use ceramic HV FT insulators to bring the single common line from the plate caps / parasitic suppressors to the upper deck.  The upper deck will allow mounting of all the tank capacitors.  The HV RF choke will be on the same lower chassis as the tubes are on centered between the two tubes. The grid circuit will be beneath the tubes on the lower chassis. 
We shall see how it all works out. The CG-309 will serve as the plate iron.     

Thanks again for the comments on the sockets.

Joe, GMS   

In some cases, I'm singing to the choir here:

The Eimac SK-500 aluminum socket was designed for forced air from a centrifugal pressure blower, not a less forceful fan or inadequate blower.  With adequate pressure, plenty of air is circulated around the tube base seals and up the chimney annulus. 

Q= AV ;  air quantity equals area times velocity across an orfice.

With adequately designed blowers, with piping at least equal in diameter to the socket cooling intake, pressure is constant from the blower outlet right up to the first real restriction, regardless of the piping and angles encountered, less some small turbulence drop.

Notice that in the SK-500 their is no socket mounting flange in the airstream.  The pins engage cylindrical sleeves inside the cavity.  So the 5 each, 1/2 in. holes and the center 7/8 in. hole in the tube base itself is the first real restriction.  They are designed to allow air flow from the center of the tube ( the vacuum seal tit) and around each of the five pins.   And yes, by all means the proper chimney or equivalent lantern glass of the right annular diameter is required.  In the Eimac chimney the top is rounded thus deflecting the air flow around the plate cap seal.

You can find a bronze SK-500 instead of the aluminum. It can be pretty nice.

But your voice is welcomed OM!  Hope you and your wife are doing well.  Missed the one on one eye ball QSO this year which happened last year at the Slab Bacon's.

Thanks for your perspective on the 4/1 tube sockets.  I have some nice squire cage blowers that work well under back pressure conditions.

73,
Joe, GMS 

OK on the sockets, Rick.

You mentioned turbulance.   Over the years I have run tests and tried a lot of air techniques. It seems that turbulance can have a big effect on efficient air flow.  The eddys and cross currents can really stifle our flow sometimes.

I remember opting to use smooth fiberglass 4" hose one time cuz the ribbed plasdick hose caused less flow due to turbulance.

I've seen the effect of using a non-symmetrical tube layout that caused some tubes to hog all the air due to pressure pockets and turbulance.

That's why I like to use a small sub-chassis with a direct path for air flow, with no bends or restrictions except for the actual tube openings.  

Another problem with obstructions is noise. I once ran a 3CX-3000A7 that had a loud high-pitched whistle.  I never found the reason for it after a lot of effort. Seemed to be coming from the tube fins. The only solution was to run it at a certain air speed to reduce it to tolerable.

With my new 4X1's in the RF deck, I tried the blower last night and hear a soft air rubble. There is something going on in there, perhaps related to the wiring and components underneath. A direct air connection wud be bettter, I know.    Air noise on ssb is usually tolerable, but on AM low frequency rubble or high freq noise will pass thru. On ssb it may be filtered out.

T

My question is to Tom or others who don't like the sound of blowers etc? Did anyone here ever consider using water cooled tubes? There are equivalents of the 3CX3000A7 out there plus smaller versions used in the chip manufacturing industry.

I don't know if the distilled water that you can get a grocery stores for use in irons or for batteries is pure enough? I also have read about using pure antifreeze. Seems to me a small volume water pump would work. As a matter of fact I have seen such systems on eBay for cooling laser systems that have all the hardware including the radiator etc. You could go GREEN when such a system is attached to your home hot water system ;D ;D ;D

no reason to deal with blower noise these days. I have this hooked to the hot tub.  ;D

Hi Terry,

I did recently look into water cooling for the new AM rig, attempting to run silent and deep.  One of the guys here does it for a living and told me what I needed to know in addition to having some used tubes and sockets. After learning the full practical real-whirl requirements, I decided the infrastructure was more effort and expense than it was worth.  In contrast, air cooling is just a matter of a blower and your're done.  The water cooling is not as easy as it sounds, I'm afraid.

I decided to run the blowers at a slower speed using a Variac and monitor the temp closely. Also, I have a lot of plate dissipation available which will permit the tubes to run cooler.  The real solution wud be to move the rig at least 10' away. Some day I may do that.

T

Pretty slick, B!  That looks like it is set up for 80M from the taps on the tank coil.   But if the impedance is low enuff, judging from the double plate chokes and double vac variable caps, it might be 160M.  There's a lot of BIG guns on CW down there.  IMD would not matter on CW.

From what I learned, the reason for the extra run of tubing around the inside of the amp is cuz there is a certain voltage per foot of insulation.  If it were 1 KV per foot, you'd need 4' of hose for a 4KV amp, etc. before it could be touched outside safely.

There are other ways to do it like using PVC pipe to enclose the water hose and run it directly out.  


Another consideration is how clean are the water-cooled tubes?  I was told many are designed for heater use at 13.9 Mhz, but still others are used in big mofo audio amps.  I never see published IMD specs on these watercooled tubes.

In contrast, the linear air cooled tubes are quite well documnted for IMD.

T

Who was the buzzard AM guy that ran water cooled tubes with a closed cooliung system that used glycol circulated thru car radiators with electric fans on the outside of the building???   It is a memory from my childhood

Cool water amp  pix. I like it.  Noticed the extra run of tubing.  I guess the voltage gradient is on the inside through the water stream. Yeah, pure water is an insulator. ...but add just a pinch of salt and your in for a super scrubbing in the ol' hot tub.  I always liked looking at the glass tube illustrations of yore in the Eimac literature.  Hey, why not go boiler?  ;D
Look at the advantages. Takes a lot of heat to go from liquid to steam.  You could have bubbles while you bathe.  " Mom, check out my lobster red tan!"

Thanks for thoughts joe. We are doing reasonably well. No change though. Yeah, miss you guys over there.  Sounds like your having fun whomping up a 4x1 design.

Tom, yes your using the pipe organ pressure box design.  The box is at constant pressure, a reservoir box so to speak (sing   ;D ) and all the little pipers don't affect it much unless you blast a 12note chord.  Interesting remarks on your singing tube.  I think your right; the vanes were resonant at a certain air flow rate.  Laminar flow is always preferred to turbulent in a system if you want oversize diameter, easily modeled results.  But again, if you want max. Flow, messy and loud, you use a constant pressure system, where flow quantity is dependent more on the pressure than the friction of the delivery system.

I keep talking to myself to get this thing built into an operational amp and not a college display. It still needs a filament blower but at least it is almost instant on.

What do you use for a water system and how much HV can that hose and distilled water handle?

Carl

WOW,

There is some great stuff going on here!!

Nice layout on the RF deck T. It looks very RF efficient in layout and design.

On the waves - - - G

Way cool. Where do you get stuff like that?  Yeah, big flanger with w/c and blower ( for bottom seals I suppose). Tap water pressure and moderate flow rate ought to be plenty.  Distilled water, and changed out to prevent copper ions from running around, heh, heh.

Well, for starters get the TMC GPT-10 k  RF amp. Tank coil assay. Complete with band switch good for 15kw , 2 to 30 mhz , currently being offered on eBay.  A couple of vacuum variables and your on your way.   Don't think 1.8 MHz would be much of a stretch.
I'd attache the link for the coil, but this d..n iPad is too awkward.

Pic #1:  First light!

Pic #2 - check this out - I welded up a rock-solid, permanent lazy-Susan pedestal for the RF deck to make it easy to work on.  It can turn 310 degrees and give EZ access to all parts.

I still have dress up work to do on the RF deck, but it is wired and all the component modules have been tested. All the supplies, keying, filaments, neutralization, pi-network, etc are working FB.

Need some nice knobs for the front panel - maybe on eBay or at Deerfield...   Still need to build cabinets for both units.

I really do like the pedestal effect and find myself pushing it to different positions for some reason.... ;D

Now onto the modulator deck.  After careful thought, I've decided to stay with the 4-1000A modulators, tetrode connected.  I will run the screen voltage regulated between 500 and 1000V to give the option of running class AB1  or AB2.   AB2 will generate more audio power when needed, though with grid current - not as clean as AB1.  With 10 dB of NFB and the solid state audio driver, it shud be a clean lash-up.

T

As the whirl turns:


Check out the new vacuum antenna relay in pic #2.  I got tired of blowing out receivers due to relay air gap arcing.  This one cost me $329 but is the best out there. Notice the effort to keep the mechanical strain off of the terminals. Still need to finish wiring it. Luckily it was the only part I needed to buy for this whole project. Good junk box here.

I ground-strapped all the RF components together, C1, C2, etc., so there will be little currnets through the front panel, etc.

The relay towards the back with the copper straps is a 160M .002 uf cap padder that gets switched in for C2 when needed.  

Towards the rear-bottom are the grid and screen supplies. They both use Variacs.  The RF deck grids use a regulated -95 fixed voltage and -120 volts of grid leak bias.  Total about -210 volts for class C operation.  The regulated fixed bias prevents RF rectification "creep" due to charging of the  bias supply from the RF grid drive.

Thanks for the comments, Big G!

I wish it looked as good as your old 4X1  X 833As.

Say hi to "TC" and the rest of the Salt City Rockers for me...  ;)


------------
Pic #1:  Notice the short leads from the bandswitch to the coil.  Copper strap rules.

Pic #2: The monolith from "2001 - A Space Odyssey "

And, of course, Yaz had to get into the act. " Could you get away from that darn workbench and take me for walk?"

I hope to have the full rig working and on the air before Deerfield, about 3 weeks away.  Lots to do yet, especially proofing and testing  - and IMD and THD optimization.

T

T

Rig looks good.


Something I'm not getting,  a week or two ago we were looking at painted empty panels.  Now an almost completed rig is pictured.

You build a rig, it takes maybe a month,  I build a rig and it takes a decade.

I have to speed up my work.

Fred

T,

Whare ya gonna put the chicken??


klc

Hey Freddy, get this...   He's not even retired like you. ::)

He still works (yeah, a few hours, possibly daily), takes Yaz on a daily
stroll  through the woods and still produces big rigs, from scratch, in
a few weeks!  :D

Maybe you need to acquire a nice Springer Spaniel... ;D

And, it's not over yet. The real pain is about to begin.

The JJ Rule of Symmetry states:  "It usually takes as much time to troubleshoot, test, modify, optimize and perfect a homebrew rig as it took to build it in the first place."

It took us 200 hours to build?  Expect to spend another 200 hours testing, modifying and optimizing.

This is a proven scientific fact that may be nominated for the Nobel Prize in Quackery any day now.   ;)


T

Knowing my luck with radio gear, it would take me about 2 years to build it, 30 minutes to blow it up on the first run, then 2 years till I managed to get around to fixing it. I saw a 4-1000A today at the York, PA hamfest, should've got it but wasn't too sure about it by the looks of the glass, and that was the second time I saw that very same tube for sale, it was at Timonium last weekend (so was probably 90% of the rest of the stuff that the same seller had). Should've got the 50 cent 4X150A too, even if it would've turned out to be a dud, it still makes a cool paperweight.

Ralph,

That's what I'm beginning to think.  I'll bet that Yaz is doing some of the construction when Tommy is sleeping.

That dog has to be good with a drill motor and screwdriver...judging by the amount of radio construction that happens around there...

Nice workmanship.

To water cool a tube, you need to keep the leakage current through the hose under a milliampere DC. Eimac and RCA used to have recommendations in their info. My experience is to keep it under 500 uA per hose. But this is for 24/7 long life gear at higher voltages that hams want to use. If leakage is high, expect slow electrolytic action that will eat your plumbing fittings at each side of the water pipe (HV and grounded ends). How to know what you have? You need to know the resistivity of your water, usually measured in Megohm-cm. There are instruments that measure this. Or might try and get a water quality lab or friendly chemist to do it. They usually measure conductivity, which is inverted of same number. Or rig up a piece of hose of known dimensions and a high R meter and measure it. Typical values to use are 0.5-1 Megohm-cm, or higher. Knowing the HV DC, you can calculate the resistor that your water pipe is, in ohms per cm length, using the area and resistivity. Then just make the pipes long enough, roll them, curl them, etc to get the value that will keep the current below the threshold you decide. If running deionized water, be sure to stick with copper or stainless steel, sometimes brass for fittings. I avoid PVC pipe due to the chlorine ions it has. It only takes a little bit to turn water into a conductor.

Some guy had a 4-1000 at a hamfest with rather dark glass. Isn't that a measure of use? His price was $100 and he claimed it worked as new, but he kept after me to buy it and near the end it was $40. if there had been a way to check it, I'd have taken it but the situation seemed suspicious and in those days $40 was 2 tanks of gas in a 455-powered cutlass.

For the pros:  What's the story on the darkening of glass in big tubes, either around the plate or at the top and bottom where the electrons presumably can escape or 'leak' past the plate?

Yeah nice amp job, but I have a question.

How come all the parts are squeezed together on each deck? Is this a mobile amp or something?  :P

A mobile amp.. HA!   I see what you mean.  Though if you pull the cover off any modern ham amp, you will find it is much more compact than this. The exception is a broadcash rig, of course.

 Yes, it was something like a jig-zaw puzzle getting everything to fit in.  Though, a picture doesn't do it justice and the rigs are actually bigger in person - and every part is easily removed without a problem. There is no layering of parts.

Being a one-shot project, I did not make a mockup or prototype.  And things change as the project goes on and parts get added that take up more room.

But compact is certainly a good thing for RF, since we want short connections and parts close together.

But I think the main reason here for a compact layout is because I started with a standard 19" wide panel, and made the depth of the chassis for the longest rack I have, which is 29".   So, except for the height, which is already pretty high at 29", I really couldn't go much bigger.  I needed to fit the parts into that limited space.

Another thing -  I put all the low voltage power supplies, fil transformers and associated modules in too. Bottom line there are only two units for a complete class C plate modulated rig. The HV supply, which is as big as the rest of the rig, is already built and on the other side of the room, used for the other rigs too.

Fabio I, had modules and power supplies scattered all over the place. I wanted to do the opposite with II.

T

Tom,  I think John/JN had it best with the layout seen in

The Bayou Desk Kilowatt

(http://amfone.net/Amforum/index.php?action=dlattach;topic=33848.0;attach=37315;image)

Oh, the humanity!

A JS rig contest would become a popular topic.  Post legit photos of real rigs that border on sure death.  (To show how NOT to do it)

T


** I just received a few pics from another 4X1 X 833As rig owner.  Never saw this rig before. They are a proud lot, these builders. Not many homebrew 4X1s plate modulated out there these days.

Notice he did it up in Ole Buzzard Black.

That was sitting on the floor in an electronics surplus shop in Manchester NH pretty much hidden in a corner.
It never had HV applied and it was used as a display/teaching item at the local technical college. Only the filament was lit along with a flow of tap water; I had to flush out the crud from the jacket

What you see is exactly what was used, right down to the filament transformer, socket, blower and foam shipping support. The tube alone is worth $1300 as a core and I paid $90 for all :o 8)

Carl

The tetrode-connected 4X1 modulator is all wired and most circuits have been tested.  It features a regulated screen supply with cooling fan. (See heatsink)  

The mod iron and Heising chokes are all mounted on the chassis. Castor wheels used to ease movement.  Notice the HV resistive divider for monitoring HV. Also meters for fil, AC line and normal tube currents.

The modulator requires the input from the GFZ-designed solid state MOSFET audio driver unit into the 4X1 grids. This provides grid bias as well as audio drive.

Other than PTT, AC power, audio drive and HV, the unit is self contained.

There are spark gaps on the mod xfmr pri and sec, as well as on the Heising reactor.  The reactor is 75 Henries.

T

Top views and the business end of the mod iron...  That's an RCA 1KW 2.4:1  mod xfmr.   Weight: 144 pounds.

Can you see why I needed those sissor trays for "extra" parts?

Pic #1 -  Lower left is the audio negative feedback ladder that taps the sec of the mod xfmr and feeds it back to the low level SS audio driver. About 10 dB of NFB when adjusted right.

The mod xfmr, Heising reactor and Heising cap are all floating above ground and each other using Plexiglas.


Pic #3 -  The shack is a mess, but that's the price of progress, I guess.

I still need knobs for both decks.

T

While we're at it, keeping with the color scheme...

Pic #1 - Dr. Love

Pic #2 -  Fabio, the 8877 linear amp

Pic #3  -  Mr. Clean - 4CX-350FJ  class A linear amp


The 4X1 RF deck and modulator will have the same black lettering once I get caught up.

They showed up today. Regular visitors to the back yard.  Sometimes up to ten birds,  they clean out the bird feeders in a matter of minutes.

Mr T,


Your prolific transmitter creation reminds me of:

http://www.youtube.com/watch?v=qS_LwObwXAs

A day in the life of VU..

(Nice turkeys! Got about 13 that show up here)

Tom, nice work!  Will you ever build a permanent transmitter? 

Eric

Thanks, Eric !

Probably the longest I've ever kept a homebrew rig going is five years. At that point my homebrewing skills evolve and I want to tear it down and do better.

In the last ten years I've gotten access to scrap yard aluminum, bought a drill press, bandsaw, lathe, etc.,  so this has caused me to tear down and rebuild the complete station several times since.

As usual, we think we are done, but I doubt it... ;D     I've been working on these series of projects since November and am pretty well burned out from building.  Just need to optimize and test everything and hopefully do some operating.   For this AM project I still need to set up the sequencer, audio driver and interface it all to the station. Then testing, testing, optimization.


Jeff, I wonder how many people over 40 use those 5-hour pep drinks?  After giving up coffee, cigarettes, coca cola and all those other stimulants, one of those pep drinks would send me speeding outa my mind.  

My secret to production is to do a little each day and stay focused... even if I am not in the mood. It adds up over time. Even one hour a night after work can knock out a full blown amplifier in a month or two.   For some reason, when I have a hot project going, I just can't sit and talk on the air until I finish it.

T

Yeah Tom, the energy of youth has a lot to do with it. I remember sitting on the floor for hours, up to 3:00 AM building stuff, parts scattered in a trail of solder splashes on the rug of the boarding house when I was in college, not even realizing I'd missed meals (as I created a very long sentence here).  ;D

..Remember being so focused, I'd walk across town just to oogle at the parts in the only ham store for miles.  B&w big xmitter parts on display in the counter case..  "Uh, a 5Y3 please."

Way to go and you have a great idea for staying the course, I. E.,  Just keep plugging and sooner or later in the session, your hooked again.

Just finished testing the WA1GFZ-designed MOSFET solid state audio driver and 4-step relay sequencer.  Both checked out good.  Mounted the SS driver and sequencer on their own chassis and will make a closed cabinet for the SS driver to prevent stray RF from getting in.

Now on to inter-connecting the RF deck, modulator and other modules into a working system. Then testing.

T



SS Audio Unit to drive the 4X1 grids and  Sequencer:

More pics:

The built-in ~50 ohm simple link input to the grid of the 4X1 RF deck sometimes has an swr as high as 2:1 on some bands.  There is no variable cap or way to adjust it.   My FT-1000D solid state RF driver usually likes < 2:1 or it starts folding back.  I use about 10 watts of dead carrier to drive the 4X1.  So, I built up a simple 50 ohm to whatever? unbalanced T-Matcher to put between the driver and 4X1 input.  It has 17 inductor taps to be sure there is plenty of range.  I tested it on 10-160M using various loads between 20 - 200 ohms and it matched to 1:1 swr beautifully.

I was going to buy a small MFJ 900 tuner for the job, but figgered I could do a better job myself.  Had all the parts.

It's so much fun to have access to ready-made junk parts. Can you imagine if we had to build all these parts from scratch, tubes included?

I still need to find some decent knobs for these projects.  I'd like to get some of those knurled aluminum fancy type.  That wud be slick.

T

And the rear-end.  That's Teflon wire used for the bandswitch connections. (of course  ;D)

I was lucky to find an 18 position rotary switch in the JunqueBoxx

Now you know why it took me over 10 years to build my rig.  I made all the parts. ;D

Fred

Tom,
I got a kick out of the SS audio driver!  Its big enough to be a tube driver with a pair of 2A3's!  Looks great and can't want to hear it on the air.  Make sure you get on the air before you tear it down to build something different. 

And yes, junk boxes are wonderful things to have!

Joe, GMS   

Yeah, Joe, the SS driver turned out bigger than I expected due to the already-built power supply with the tall board.  Now I'm having a problem locating it close to the modulator deck to keep the audio input and NFB leads as short as possible.

But there's a lot of room in there to add stuff. If the QIX negative peak limiter circuit works out, I will probably mount it in there, since it feeds the SS driver anyway.


Well, I just built a diode stack for the modulator bias. It uses 140 forward biased diodes on a Plexi board and a big rotary switch.  I could use ALL bias from the SS driver board, but wanted the diodes as a failsafe in case the SS driver shorted out.  Nothing like zero bias on a tetrode.... bam!

I started the station interconnections process last night and might be ready to fire up the RF deck followed by the modulator and assorted audio stuff soon.

Picked up some aluminum sheet at the scrap yard yesterday. I'm tempted to build the outer cabinets before doing any testing.  It's scary with everything exposed, even for a day of so.


Fred, I figgered you, especially,  homebrewed all your parts for the 51 watt rig.     Reminds me of a story from 1964. I was a little JN standing at the counter at Hatry's in Hartford, a Collins ham dealer.  An older, well dressed  ham came in who had just bought a brand new Collins S line.  He said he didn't currently have the money to buy the matching power supply for the 32S3.   Corky (salesman) suggested he build it. The guy got POed and told Corky that he didn't build his own refrigerator or washing machine, so why shud he build his own power supply?   ;)     (appliance operator circa 1964)

T

If the QIX negative peak limiter circuit works out, I will probably mount it in there, since it feeds the SS driver anyway.

Well, I just built a diode stack for the modulator bias. It uses 140 forward biased diodes on a Plexi board and a big rotary switch.  I could use ALL bias from the SS driver board, but wanted the diodes as a failsafe in case the SS driver shorted out.  Nothing like zero bias on a tetrode.... bam!

It's scary with everything exposed, even for a day of so.
[/quote]
----------------------------------------------------------------------------------------------------------

Now when doesn't one of Steve's circuits not work out!  If its his design I am sure it will do the deed!

Wow, that's a lot of diodes but I understand why your doing it.  I believe your using the 4/1 in a triode configuration.  If you were using them as tetrodes, you could dump the screen voltage if you had excessive plate current.  A DC referenced resistor in the negative lead of plate supply ground referenced would be a great reference to use to set a trip point circuit which in turn would drive a FET to disable the screen voltage.  

Your lucky to have a good source for sheet metal!  The old buzzard rigs of the 20 and 30's were commonly open frame construction.  Its amazing how many of the OT op's survived.  Just have to pay attention and mind your P's and Q's!

Joe, GMS
      

Joe,

The tubes are in tetrode config with regulated screen voltage.


That trip circuit is a good idea.  I already use it for the linear amps using a negative lead resistor sample.  I might later add it to the modulators too.


The QIX NPL already works FB on the PDM board. I'm simply adapting it for 4X1 modulator use. It's a pair of clipping diodes followed by an 8 pole low pass filter.

Later -

T

Just a note  ;)  That low-level negative peak limiter is not as effective in A.C. coupled modulators (like this one) as it is in D.C. coupled modulators  (like a pulse width modulator).

However, it will still have an effect.  The key with an A.C. coupled system is to absolutely minimize waveform tilt and/or overshoot.  This is best accomplished by ensuring the frequency response at the low end is very good, and the response throughout the audio range is flat up to the cutoff point, and then rolls off, etc.  If the transmitter will modulate a 30hZ square wave, it should be reasonable.

The N.P.L. will cause a DC shift to occur, and in a D.C. coupled modulator, the DC shift is propagated through the system, and the reference point does not change.  With A.C. coupling, the reference will shift down as the D.C. shift is mathematically integrated.  The better the low frequency response, the more time it takes for the integration to occur.

By the way, the rig looks great.  It'll be interesting to hear it on the air, that's for sure!

I'm building a 16 MOSFET rig for Rattlesnake Island, mostly to improve the signal on 160 meters for the Grey Hair Net.  Should be on the air soon.

Regards,

Steve

Steve,

Cool on the 16 pill project for Rattlesnake.  That should get you back up to par when away... ;D

As far as audio respone... the last Fabio generated very close to e-rig shark fins once I had it dialed in. I'm using the same mod iron, SS audio driver and NFB, so hopefully the NPL will like it.

Well, other than building the cabinets for Fabio II, I've finished the internal wiring and interfacing it to the shack. Ready to do some dummyload testing next.  It's always scary when we must apply the HV for the first time.  It's hard to imagine, but technically, if everything worked and was dialed in correctly, the rig could have a QSO right now. But we all know that could never happen except in the Bizzaro Whirl... ;)

Just finished installing the panel lettering labels - my favorite part of the whole project! It really brings the rigs to life.  The band switch lettering still needs exact 160 - 40M labels once tested and found.


Check it out:

T

Notice the solid state audio driver to the left, the sequencer to the right and the T-Matcher in the center. All parts of the project.


You'd think I'd break down and buy some matching knobs...

T

Pic #3:  It all started on April 4th, a little over 3 weeks ago.  My goal was May 4th, to be completed before Deerfield.   But testing and debugging usually takes as long or longer than it took to build.

It's amazing the progress on Fabio......from cut front panels to a living breathing machine.
The RF output will be kept secret and we calculate from plate volts and current what's gonna come out to the aerial?

Looks GREAT Tom and can't wait to hear it on the air.  Should be very effective at puncturing absorption !!
Joe, GMS

Started checking wiring and firing things up.

Found two wiring mistakes in the modulation transformer / Heising choke area. Fixed. What a space shot.

Disconnected the modulator from the RF deck.

Into a dummyload, fired up the RF deck for the first time. At 2KV only 50 watts out and the plates were getting bright red. No way to resonate.  Felt the plate choke and it was HOT.  I had wound my own and it either had a resonance or the wire I used might have been nichrome... by mistake. It had a resistance of about 40 ohms, though I wouldn't think 40 ohms in the plate circuit was that much.   Rewound a new choke with Teflon wire. Less than an ohm.  Fired it up and the plates were gray and put out reasonable power.  Nice, sharp plate dip, screen peak and power output peak. Neutralized.

Then the screen shorted out. Turns out a .001 1KV disc shorted. I forgot that after the screen self-modulation choke there are large EMF collapses when unkeyed.  I replaced the .001 with a 5KV and all was FB.  I put my VOM on the screen lead to monitor and blew out the VOM. Again, forgot it doesn't like spikes. The real problem was that I should key the driver on near to last using the sequencer. I had the driver turning on before the amplifier. Doing so cured all spike action.

Getting late so shut down for the night.   I can see it will be slow ploughing, but that's how it goes.


Question:  I added Plexiglas windows to the 4X1 viewing holes.  If the tubes are 2" away will 1/8" Plexi eventually deform?  It doesn't seem to absorb heat, just like glass, but I seem to remember having a problem once...?

Ques #2:  Does anyone use spark gaps across their screen modulation choke?


T

Hi Tom,  back when I used modulation transformers, etc.  I had a spark gap across the modulation reactor.  In fact, I seem to recall it came that way, but my memory is a little foggy there.  Wow, that was a long time ago (we're talking 35 years ago or so!).

Hi Tom,  A good source for high temp capable and RF blocking "view ports" are defunct microwave ovens.

Here's the RF deck /w a microwave door panel. It is a re-package of an RCA BTA-1R1 I did a while back:

(http://)

Hi Bill,

That rig is quite a piece of art!  Is that part of a plate modulated BC AM xmitter that now covers all the bands?  Or maybe it was modified into a linear?

OK on the microwave glass.  I will monitor the Plexiglas and if it starts to distort, I will look into the microwave stuff.


Steve, OK on the Heising choke spark gap. Yes, I use gaps on both the mod xfmr and Heising reactor, but was wondering if anyone used a gap on the screen self-modulation choke.  When the keying sequencer is wrong the screen circuit lets out quite a snap which could potentially damage tubes and parts. The gap wud be just a precaution in case of trouble again.

I have the 4X1 running DEEP into class C right now. Normally -200V of total fixed and grid leak bias is required, but I have stepped it up to -285 volts. I see no plate color, though it is a little harder to drive, like 25 watts vs: 15 watts.   I wonder where it crosses the bridge to become class D?


T

you would have to cross way more then a bias bridge to get there. would have to take a detour down input lane and get all squared up.  then do some road construction after the first bridge on your left.

awesome on the transmitter. did you play any with just using minimum fixed bias and getting ya mo volts from addition grid leak resistance? and see how it does on the clean tests?

Tom, thanks for the kind words.  It is a 'repackaged', frequency agile BTA-1R1.  The boss wouldn't let me take a chainsaw to the doorways so I brought it inside one piece at a time and rebuilt it into a standard 5' rack cabinet.

(http://)

I would rather have a re-packaged BC TX than the huge cabinet and chrome. That is a nice maul.
Fred

You're quite a craftsman, Bill.  What a novel idea - to take a FB BC transmitter and convert it to a smaller package to fit into a 19" rack.  Amazing you got it all in that cabinet. Does it include the mod iron and HV PS too?  


Brandon -  I have barely started testing. Just able to get a dead carrier out and slowly fixing little problems and making mods as I go along.  This is possibly the most difficult part of building a rig, so taking my time with it.  I want Fabio II to perform perfectly and cleanly when done. It may well be my best rig ever, if it comes out right.  Blowing out expensive parts along the way ain't on the agenda, hopefully.  

T

I hear ya man. It will be awesome to hear it on the air this fall/winter. I always love and hate that nervous feeling of running something you just put together. It seems like every little smell or sound can send you into a panic looking for something getting hot or not doing what it is supposed to do.

Thanks for the pictures and updates.

Hi Tom,   everything fit in the 5' rack.

Bottom level has HV supply and mod transformer,  middle level has mod reactor, LV and bias supplies, overload circuits, etc. 

Most of the heavy stuff on the bottom.  The angled cable is to correct a 'twang' in the cabinet - apparently the thing was dropped on it's way to the dumpster and the backside was quite out of square. I tried to 'squish' it back to square, NG, so used the cable & turnbuckles.  Less of a mess than cutting and welding - and hidden inside.
(http://)

Mid Level - mounting the mod reactor here required some bracing of the mid level plate (1/4" aluminum). 3/8" steel threaded rod runs from mid level aluminum plate to the bottom rack plate which is 1/4" steel.
(http://)

All the layouts were done with a CAD program (DeltaCAD).  Lots easier to move electrons around than 100# hunks of iron!  Created full sized drilling templates for the interior plates, the RF and Mod chassis, and the front panels.   
(http://)

Hi Bill,

Pretty cool using Cad to lay out the optimum fit for your rack. You sure have a nice organized rig there.

Well, here's the update on Fabio II.  I have run some THD linearity tests. I hope to posts some spec analyzer pics soon. Seems the audio negative feedback is doing its job and with some tweaking I am seeing -35 dB second harmonic and about -50 third harmonic numbers. This is quite good.  Just like my linear amp project, by adjusting parameters I can dial in better cleanliness.  Screen voltage and current, plate tuning and loading , drive levels and NFB all have an effect on THD.

The problem now is I am getting a spark on the mod xfmr secondary arc gaps whenever the rig is unkeyed.  I don't dare raise the HV above 2KV until I solve this.  I've tried a lot of things to cure it, since  I've had these problems before with many rigs. So far the sequencing, delayed relays and all that have not helped. I also tried less fixed bias on the RF final so that it doesn't fully cut off. No diff.  This worked on Fabio I before, but not this time.    

This sequencing is a bear cuz if I play around too much I get catastrophic crap-outs.  When I added too much driver delay, the RF final 4X1's flashed over and made a light show of blue and yellow. I thought I wasted the tubes, but after replacing a shorted .01 filament bypass cap,  everything worked FB.  

I have to hand it to the guys who have built big plate modulated rigs and got them tamed. It's not an easy thing to do.  A rig will tend to beat us up in areas where our knowledge is lacking. It somehow finds these areas. As much time as I have spent in the past with proper sequencing, it always haunts me.

Right now here's the sequence of events to key:

HV always on.

Key on:

1) RF antenna relay switched on (vac relay)
2) RF amplifier turned on via fil CT ground.  (I've tried caps here and use a 56K resistor across the contacts.)
3) Driver on
4) Modulator CT grounded on.  
5) Low level audio turned on

It works FB on keyup.

I reverse the above to unkey and all FB until the end and I get an arc across the mod xfmr gaps.  The Heising reactor is dumping the power, but not all - then it arcs to dump the remaining stored power.  

I will look into it further, to see exactly in what step this arc is occurring. But hopefully I will not need to key the HV to soften things.  As a last resort I will put a longer delay on the ant relay release.  I've tried most everything else.

BTW, the arc still occurs when the low level audio is completely disconnected from the modulator.

T

T,

Vacuum relays for antenna switching are FAST mechanically as opposed to open frame, etc. I have been going through the same issues on an old buzzard homebrew here . (pair of 4-400's by 849's).. what cured similar arcing was delaying both the antenna relay and rf drive on release.. The difference is that the plate primary is also part of the sequence for HV.. it all drove me nuts!  BUT this is the fun stuff! enjoy

OK Jeff -

Yes, it is a tough game to get the sequencing so right that there are no arc gap snaps.

Exactly where does the power from the Heising reactor supposed to go during unkey?    Do the modulator tubes absorb it or does it go thru the RF final that needs to conduct current to in turn  dump it into the antenna?

I just ran some more tests and still stumped.  I made the ant relay longer, but no change - still arcs at the mod sec gap.   I delayed the RF final CT keying relay.... no change.

I disconnected the SS audio driver and grounded the modulator tube grids - no change.

I also toggled the modulator tube keying off so they did not key up at all - same thing, arc.

Already tried caps across the cathode bias resistors on both mod and final. No change.


Tried keeping the RF final on with no fixed bias. I could see the tube plate current spike on unkey, indicating the power was being dumped into the final -  BUT there is still an arc.  I opened the arc gap a little more, but it is at the limit for even double the working voltage. Something not right.

T

Tom

Probably always better to key on and off the HV power supply.  Opening the CT on filament xfmrs leads to sudden current drop-out in the wrong place in the overall current path.  Doesn't surprise me that you shorted a filament by-pass cap. The back emf from the big reactor will cause arcing.  You avoid these problems by allowing the current to decay more slowly by the time constant from the HV caps in the power supply.  You'll need a step-start for the HV power supply.

I think you mentioned previously something about the screen by-pass cap shorting.  Probably just another problem caused by your method of keying the xmtr.  I also think you're using a reactor in the screen circuit, sudden collapse of current in a reactor causes big back emf.

You still need proper timing other parts on the xmtr.  Especially the antenna relay, it should be first on and last off.  Drive should be up to full drive slightly ahead of the full HV.  A delayed step-start HV supply does this.  I think audio drive to the modulators can arrive any time.

Just a few of my thoughts,

Fred

Sequencing theory ..all goes to pot with the BIG mauls in practice  ;D.  hopefully everything should get dumped to the antenna, ( load) .. but what value Heising cap are you using, and what configuration of modified Heising is it? and what circuit changes have been made vs the old Fabio ? baby steps OM  :)

JJ,  (Jeffie James)

OK on the antenna taking the collapsing power.

I'm using a 1uf Heising cap at 10KV.    Heising config?  The mod xfmr bottom sec connects to the Heising cap and then the cap to the Heising reactor bottom. The top of the mod xfmr sec directly to the Heising reactor.

I am using a standard 1 ohm to ground floating negative lead back to the HV supply to monitor grid current when using the linears. Hope that is no a problem. I didn't use it with Fab I.

With the old Fabio, I did not use a sequencer, rather dicked around with delay caps on the various relays. It took some time but using CT keying I got it right.  But I thought this sequencer wud make it easy.

Just ran some more tests. Nothing worked.  Tried making the driver stay on longer. Tried the ant relay on longer.  Made the RF final draw current all the time by reducing the CT resistor from 50K to 200 ohms.    Tried the modulator tube idle from zero to 400 ma.... no difference.

And I tried a combination of all these things.  The only thing that seems to reduce the spark to near nothing is to reduce the power down to 1/4.  The collapsing field is smaller and does not bang the gaps.

Other than do a step start HV thang, I'm about out of ideas.  

The thang that bothers me about the step start is I am using about 100 uf of HV filter capacitance.  I wonder if that is too high to drop real fast in a second?   I do like the idea of going back to a step start
though. It's safer and I cud also use it with the linear amps...

Fred, yeah there is a lot of bapping going on with the CT keying. Worked with Fab I and great wid linears, but maybe I need to change to HV keying for the plate modulated rig.

T

Where would you put the two clicks of HV step start into this key up sequence?   (The initial start and the final voltage)


Key on:

1) RF antenna relay switched on (vac relay)
2) RF amplifier turned on via fil CT ground.  (I've tried caps here and use a 56K resistor across the contacts.)
3) Driver on
4) Modulator CT grounded on.  
5) Low level audio turned on


Key off: Opposite of above


I assume  #2 and #4 would always be keyed on when using HV step start?


T

http://amfone.net/Amforum/index.php?topic=31731.msg247041#msg247041

Bruce's fine sequence with HV primary switched in the mix..

and Heising configs.  I use #2..

Tom

Looking at your line-up, it seems that you should have the drive on ahead of the final.  You have the reverse of this, steps 2 and 3.  Also, no reason to not have the modulator come up at the same exact time as the finals.  With the mod tubes not on there is no load on the mod xfmr when current starts through the mod reactor to the finals.  At a glance, to me that seems like it could be problematic.  In reverse order, you're removing the load off the mod xfmr by opening modulator CT and then after that event you open the final CT.  Big back emf with nothing to absorb it.

To answer your question, antenna on, drive on, HV step-started on to both finals and modulators and then audio drive last.  I'm assuming that you're using some or all self grid bias or maybe some fixed grid bias.  You need drive to limit the plate current, that's why I think drive should be on ahead of the finals.

You're right about step-starting the HV with 100ufd cap.  Is it one cap or number of caps making up the 100ufd??

Fred

Jeff,

I am using #3 from the Heising diagram you posted above.  Do you think there is a difference in better bleed off using #2 vs: #3?    Maybe the Heising cap going directly to ground is better than the hot end of the HV supply, I dunno.  Remember that I am using a negative floating HV ground for metering. (one ohm)

Fred, I tried keying the driver first and had fireworks.  The screen arced badly as well as the mod gaps.


After doing even more relay delay, etc tests last night, I've tried about everything that has worked in the past.  No choice but to go to the HV keying idea.  That HAS to work, even if I have to leave the ant relay on for 5 seconds... :-)  With HV keying, the modulator and RF final will always be keyed and sucking power if I have the drive on so eventually will bleed off the EMF.

Using Bruce's method I would also need to key the RF screen. That will require a HV relay of some sort. I may have to key the modulator screen too.


I have a pair of 240V AC contactors I may build up...

T

Tom,

I use #2 Heising.  You're using #4, you may get a better bleed off of the back emf from the reactor with #2.  You'll have to try it to see if it helps.

I mentioned the RF drive only so there is enough bias when you power on the finals.  This would have nothing to do with the arcing.

Not sure if you have tried different sequences on the up-start but,  I think you have the finals and modulators wrong.

IMO I think you need to turn on the modulators before the finals, you're doing the reverse of this.

Try this line-up.

1,  antenna on
2,  modulators,  this puts a load on the mod iron.  At this point with no audio drive you don't need any load on the mod xfmr secondary.  So it doesn't matter that the PA is not loading the mod iron.
3,  RF drive
4,  final PA
5,  audio drive to modulators

Key off, the reverse order.

When you un-key the finals the large back emf from the reactor passes through the mod iron secondary.  The modulators, at this point, are still drawing some current which keeps a load on the mod iron primary which keeps a load on the back emf.  This may reduce the arcing.  It may be worth trying this.

Fred

Tom,

After reading you're comments about the screens.  If you remove the HV from the plates you must remove the screen voltage.

Another scheme to consider,  you can turn off the modulators and the finals by simple removing the screen voltage.  Without screen voltage you could leave the HV on to the plates.  The output from the tubes should drop to near zero without screen voltage.  Although, with 4-1000s you would have try this to see what output may still come from the tubes.

Fred

    Just arrived at a San Antonio Hotel as part of a three day business trip.

Heck, back in the 1980's when I ran a 1 KW DC input final, I use #4 Heising configuration with the cap on the top side. Back then few if any used a sequencer. I just keyed things, and seldom had a problem with flash over. Rigs back then had a distinctive 'Ker-Klunk" which was a give away to who keyed up. Some folks didn't even have to speak. The "Ker-Clunk" followed by 60hz hum during a QSB fade meant a BC-610...

So reading Fred's last post, I think keying the screen might do it. The back EMF spike will be a positive going spike above the B+ level. If the 4-1000 screen is keyed to ground, some plate current will still flow. When the back EMF spike comes, the plate should absorb it. To cut off the 4-1000 this way, I suspect the screen needs to go negative several hundred volts. So the screen would have to go down in two steps, say zero volts, then -500V.

Back to normal programming as I prepare for tomorrows festivities in a semiconductor fab clean room where I am about to rebuild an old machine.

Jim
WD5JKO

Ya know, youse guys may have a good point about the screens.  When I first fired up the rig, the screen circuit was arcing like crazy on unkey and took out a disc cap. I even added arc gaps to the screen inductor.   Since changing the sequencing, the screen arcs have disappeared.

But still, the screen may be rearing its head in the form of the HV mod arcs.  Since I cannot solve the problem with any combination of HV relay delay  or sequencing techniques, maybe keying the screen will help.  I ended up keying the screen on my old 4X1  PDM rig and this solved the problem a few years back.

I will need a HV relay since the screen is 500 V and has inductor EMF.  Jim, I presently have a fixed bias on the 4X1 RF final of -90 volts. This cuts the tube off, even when keyed, as long as there is no drive.  Should I simply add a screen relay that takes the screen from +500 volts or ground?

Would I continue to key the CT of both the RF tube and modulators  -  or instead, ground both CT's and key both screens of the RF and modulator?  (The HV wud stay on)

T

Tom,

If the tubes are cut off at -90V bias, does this mean there is little plate current??  If so, then why are you keying anything.  The tubes are already cut off.  Maybe what you should do is to increase the bias to a greater negative bias on receive.  This would allow you to leave the screen and plate voltage on.  This should eliminate all your arcing problems.

For the modulators remove the screen voltage on receive.

You would leave the CT connected.

Fred

Fred,

Correct, the finals do not conduct with the -90V on until I key the RF drive.

I have already tried what you suggested, but when the drive gets cut, the arc occurs. The HV and screen stay on. I grounded the finals and mod CT's all the time.   No difference.

I'm starting to think keying the HV with a step start along with the screen might work.  I wud ground the CT's.  Bruce sent me a screen snubber circuit that might help too.


T

I'm looking at Bruce's sequence.  He uses a slightly different order for TX vs: RX.  With my sequencer, the keyed order is the same, but reversed when unkeyed.

But what if I used his unkey order for both key and unkey?


It would look like this:

CT of both finals and modulator always tubes grounded.

1) T/R ant relay on
2) HV step start
3) Screen voltage on - for  both finals and modulators
4) RF drive
5) low level audio on

Reverse order to unkey.

I'm still not sure if the -90V fixed needs to be lower so that the final conducts SOME plate current even with no RF drive.  How else can it dump the power?  Right now as soon as the RF drive is cut, all currents stop dead.

** - I ordered two vac relays for the screens. Might as well get the screens switched, no matter what I end up with.

T

http://www.youtube.com/watch?v=hIkNY5xjy5k

tom sent me that link. looks like he almost has his spark gap dialed in.

That sequence would be correct if you use the step-start HV when keying on.  It seems, with all the testing you done, that you covered all the ideas that I suggested.  I guess when you use a big reactor no amount of loading is enough to damp the back emf that occurs when the plate current stops dead.  Also didn't realize that removing the drive cut off all plate current.

The reverse of that order will NOT work when keying off because you're removing the drive before killing the HV.  You need to cut the screens first then the HV then audio drive and last the RF drive.  I'm not sure if the sequencer can handle two different orders, one order keying on and a different order keying off.

Although, cutting the screens first may also cut off plate current and still cause back emf.  You may need to cut the HV first and estimate the time it takes for the HV to drop to a level near the screen voltage and then cut the screens.  The thing you need to worry about is having screen voltage present without plate voltage.  This causes the screens to draw heavy current which could exceed screen dissapation.

In order to keep some plate current you would need to raise the negative grid voltage to something less negative.  In fact you could use some fixed bias and some grid leak bias by using some value of grid resistor.  You could also use all grid leak bias and then you wouldn't have the lack of drive cutting  off all plate current,  you would have the opposite, too much plate current with no drive.

Fred

Looking at the sequence,  you could put the RF drive ahead of the HV then the screens and last the audio.  I think the tubes can handle having drive without plate voltage for a second.

antenna
RF drive
HV
screens
audio

Then you could just use the reverse order to key off.  But, again cutting the RF screen ahead of the HV may be a problem because it may also cut off RF plate current and cause back emf.  You may need to have a slow time decay of the screen voltage.

If you were running the RF screen from a dropping resistor off the plate voltage you wouldn't have  this problem.  I think you using a separate screen supply and screen reactor to modulate the screen.  Instead of cutting the screen voltage between the reactor and screen you could  cut the circuit in the supply before the filter caps and let the caps discharge the screen voltage more slowly.

OK, thanks, Fred.

Well, I ordered two 60A used contactors from eBay to build a HV step-start.  I overrated them in case I make a mistake and get a short.

The screen vacuum relays are on the way too.

So this will give some new options to beat this arc problem. 

I like your idea of experimenting with the screen supply by keying the xfmr primary, to get a slower decay.  I will also try switching before and after the screen modulation choke to see what works the best.

So, back to the drawing board with Fabio II for now. 

Been outside on the towers doing catch up antenna work.  I'm finding the pair of 20M  300 pound stacked Yagis are getting too much to maintain.  They are scary to work on. So in the last two days I took them down. Who knows what I'll put in place of them, but I think as I get older I will start shifting back to wire arrays with ropes and pulleys... ;D

T

COOOL!

T,

You've now taken Fabio II to new heights.. Complete control of voltage.. In fact, you have officially become the second "Electron Wrangler".. (can't tell you the first, because he'd have to kill you).. Yes "I can see it now"..

And Jeff I applaud your selection in that image of what appears to be a couple of 50C5 in shove-yank.

I've been following this thread since 2009 with some interest as I have several similar projects in mind ... I do not want to seem to be attempting to steal this thread as it is an interesting problem with so far a difficult solution ...

the problem as I see it is what to do with parasitic energy generated by current carrying inductors when the current they are carrying is turned off ... the energy in a 72 Henry inductor carrying 0.5 Amp at turn off can be roughly approximated as   E = L x i x i  or 18 Joules ... this energy manifests itself as a voltage spike of reverse polarity across the inductor as the internal magnetic field collapses

In the am transmitter under discussion ( maul) what happens to this spike is that it tends to appear across the rf amp anode circuit unless a B+ relay is used .... the value of this voltage can be approximated by conserving the 18 Joules of energy produced and calculating the resultant hv applied to the anode circuit bypass capacitor      E =  .5 x C x v x v   assuming the use of a 500 pF bypass cap and ignoring stray capacities this calculates to be approaching 268 kV ... no wonder things are arcing ... this is why the spark gaps are firing

we need some snubbers ... hv movs can be found but tend to be expensive .... consider the use of a string of say 500 V movs ... I bought a bag of them off Epay for $.25 each .... the data sheets were found on Mousers web site and I am considering the use of a dozen in series to snub a 2kV mod reactor .... when you put this many in series the usual 300 pF capacity decreases to 25 pF and will not mess with the maul's high freq response .... add a series resistor and a neon bulb and you can have a visual indication rather than the crackles of thunder on firing

I think you will need this as well in the screen reactor .... good luck .... 73     John

Yeah,  COMPLETE CONTROL with the Electron Wrangler.  That's the ticket!


But first, "If I only had a voice."  (Sung to Oz, "If I only had a brain")


"I would talk away for hours, squawk about my towers, with vocal fry that's choice.

I'd sound just like Walter - my chords would never falter... if I only had a voice."


Now all I's needs is senior anchorman  lessons from youse guys, caw mawn.

T

You make some good points there, John.

I do intend adding a snubber to the screen circuit. Bruce has suggested a series  .1 - .5 uf  and 500 ohm cap before the screen choke from hot to ground.

The MOVs sound interesting, though I know some who say they fail a lot and might be trouble.

There's a lot of things to try now that I will be keying the HV and screens.  I will look into the HV snubbers if I need to also.

It seems like a difficult task (and juggling act) to dump 70H of energy.  The transmitter plate circuit has to conduct to dump energy into the antenna - but at the same time it needs to slowly die off or this same conducting energy will have no place to go.  Like a Catch 22.

The bottom line is if the arcing gets out of hand, we will be rewinding our modulation transformer - and possibly the Heising reactor - and possible tube and parts damage.


T

Tom,

My PW version of your xmtr also uses a 50hy Heising reactor.  Like I've mentioned,  keying your supplies should solve your problems.

I step-start my HV supply (1500V) and I never had any arcing problems.  I also have no spark gaps on anything.

I don't think you need any snubbers on the screen supply.  All you need to do is turn on and off the screen supply before the filters.  Let the filters discharge the screen voltage.  You could add a few ceramic disc caps (5KV) .01-.05 on the filter caps to ground.  These caps have less inductance than electrolytics and will act faster to short any spikes that might come from the screen reactor.  Also don't use any method to open the screen circuit after the filters.  So forget relays on the screen line to the tube.  Just leave the screen circuit intact.

The same is true for your HV supply, a slow decay of the HV will produce less energy from the reactor, if I remember all that calculus that I mostly forgot.  Don't use any method to open the DC plate circuit.  So forget the cathode relays, leave everything connected.

You just need to use the right sequence for keying on

Antenna on
RF drive on
HV on
Screens on
Audio on

Keying off,  the reverse order.

The timing between the screens and HV should be close.  You don't want the absents of screen voltage to cut the tubes off before most of the HV has decayed.


With the speed at which you build stuff, I'll expect these changes to be completed by the end of today. ;D

Fred

PS to my comment about the reactor producing less energy.  The reactor will have the same stored energy but release it at a slower rate with a slow decay of HV. which should result in less of a voltage spike.

The voltage induced in a coil is directly related to the rate of change in current through it.

OK Fred -

There certainly are wide varying opinions on the sequencing.... ;D

Looking over yours again, it makes sense for my particular use. Plus it can be reversed in the same order.  Think I'll try your sequence above.  Tnx.

I'll be keying the HV primary and the screen primary. This shud soften things considerably. The RF final and modulator CT's will be always grounded.

I like that the RF drive turns off late, just before the antenna relay drops.  This will give the amp every last chance to dump the power into the antenna as the HV and screen supplies are decaying.   I will try it with and without a fixed grid bias to see what I can get away with.

The contactor and vac relays will be here later this week.

Today I added the 1 ohm resistors to the filament primaries. The 7.85 fil voltage dropped almost perfectly to 7.53 vdc at the pins. It shud be 7.50 vdc.   The problem is I under-estimated the resistor power dissipation. At 3.92 volts AC drop and 2.6 A we are talking 10 watts of heat.  The 5 watters I had in there were not happy. Ordered some 100 watt heat sinked wire wounds as overkill since they were cheap enuff..

I'm confident when the new parts arrive the arcing problem will be solved. Evidently linear amps don't mind harsh CT PTT keying while larger plate modulated rigs with their reactive EMF like to stayed keyed and bled off slowly.

I'll post more results as the parts come in and get installed..

T

perhaps we should move this to the technical forum as I intend to further muddy the waters ....

relay sequencing is a good idea for many reasons in an am transmitter but I am not sure that it can be done in a fashion that will keep a system under control with regard to unwanted parasitic energies without addressing them directly, so here is a possible solution .... I mentioned movs as they have the advantage being passive until triggered .... a disadvantage mentioned is their reliability .... were they properly applied ? .... there are energy limits as a time function for these devices

for the sake of argument lets assume that movs are not practical for this application .... is there another way to snub ?   yes since we are considering a sequencer, could we not add a sequenced snubber to the modulation reactor ....  this seems doable .... a hv relay sequenced to parallel a high power resistor across the mod reactor at the end-of-transmission just before dropping the carrier could dump and eliminate the parasitic energy .... the advantage of this that it removes the requirement of this action from the rf chain

most interesting, Mr. Spock

Well, a diode across the inductance is the traditional way.  ;D ..  You only lose half the audio.  ;D

Can't believe the length of this topic. 

Here's a method of screen protection when using the choke method from the Orr handbook, page 296, 15th addition.  This method might help suppressing back emf across the choke by tube action. Partially Paraphrasing:

"Place a resistor in series before the choke right after the separate screen supply of about 3k to 10k ohms' fig, D, and the screen supply should now be about 1 1/2 times normal with the actual value of the resistor sized that normal screen voltage is supplied at normal screen current."

"When the plate voltage is removed, the screen current will increase greatly and the drop through the resistor will increase to such a value that the screen voltage will be lowered to the point where the screen dissipation of the tube will not be exceeded."

So might this action be approximated through every current cycle, keeping inductance swings "gently" manageable in their charge and discharge?

John,

Good idea on using a relay to place a big power resister across the Heising choke during unkey.  I  think this would work.

Frank / GFZ sent me this idea yesterday too.  Wish I had heard it before ordering the new parts, but that's the way it goes.

I suppose it doesn't matter if the energy is dumped into the antenna or into the resistor, same result.

I will give it some more thought as I wait for the parts, but at this point think I will still key the HV and screen circuits via their primary 240VAC transformers and ground the CT of both final and modulator. This is how most big plate modulated rigs do it. Might as well do it right where the EMF spikes will be naturally bled off into the antenna load.   But if the new parts don't do it, I will certainly give this resistor method a try.


Rick - OK on using the resistor in the screen.  I suppose that would work for smaller rigs, but using a 3K resistor would drop 235 watts of heat across it in the 4X1 rig.  A 10K would produce 783 watts...      So solly, Mr. Orr.   ;D

T

Not really too sure that the back emf from the reactor gets bled off by the antenna.  Most of it gets absorbed by a higher plate voltage on the finals.  Of course, the antenna does add to the overall load on the tank circuit.  Some of it gets absorbed by the back load on the mod xfmr from the modulators.

The voltage spike from the reactor is a function of the RATE of change in the current through it.  The faster or greater the rate of current change results in higher voltage spikes.  So, when JJ was opening the CTs on the filament xfmrs that dropped the current about as fast as he could do it (nice work Tom ;D) he was getting the maximum fireworks.

The only logical way to reduce the voltage spike is to increase the time it takes to drop the HV which will drop the current slower.  This is also true for the screen reactor.

So I think, from his comments, JJ is going to try the primary shut-off of the screen and HV supplies.  This will allow the PS filter caps to decay the voltages at a slower rate.  This should result in much less back emf.  Hopefully this will be enough to solve the problems.

We'll all find out after Tom completes the changes.

Fred

While this is true there must be a plan B for times something unexpected happens. Loss of drive can sometimes create a fast enough decay to flash things over. I have the Tee shirt.

MY SOLUTION IS TO ACTIVATE/DISACTIVATE RESISTANCES IN PARALLEL WITH THE CHOKES

I keep all the voltages to the final and to the modulator (4 x triodes) all the time ON in order to be very fast on tr/rc. I had the same problem as Tom but not anymore. My solution is in the attached sheme and was a suggestion of Stu that fitted perfectly to my transmitter.
The on-off sequense is very simple and done manually in few milisecs by a simple make before brake rotary switch  4P4T that controls 26.5Vdc.

ON :
1st position = ant relay from rc to tr
2nd position = Rf drive on
and modulator's bias from the cutoff (-200v) to the idle current setting (-100v) by grounding the bleeder pot (only for lengthening tubes' life).
3rd position = reactor's vacuum relay opens R1= 5k/100w and screen's relay opens R2=5k/20w
4th position = audio on

OFF : oposite

It is amazing how quietly turns on and off the transmitter now.
The resistances are involved only when the Tr is off and they are disactivated when it is going to be on.

Stefano

Hi Stefano,

That seems like a very good solution.  I wish I had heard it before ordering these step-start parts - at least to try it with my existing setup.

I received the vac relays today, so am tempted to use them to add a resistor across the HV Heising reactor and the screen choke as you suggested.   Maybe I can still keep the HV on and ground the fil CTs using this technique.

I see you leave the HV on all the time as I presently do now.   Do you key the fil CT or leave the CTs grounded all the time? I didn't see reference to them in your sequencing.  Maybe you turn the RF final off with a fixed bias to keep it from drawing current. Then the RF drive comes on and still no (or little) plate current.  Does the RF final tube conduct plate current after the screen is turned on or a little current before too?  

Or maybe the RF final's screen voltage stays on all the time and as soon as the RF drive comes on, there is power output to the antenna?  IE, the fixed bias keeps the tube off when there is no RF and the grid leak adds the remaining bias during full drive power.

Then I could key the mod tubes using the reg screen supply keyed at the 120VAC point.

T

You're right about the drive.  He is using -90V bias which completely cuts off the finals.  That's why I suggested that he use some grid leak bias along with less fixed bias.  If he looses drive the tubes will still conduct some current.

Fred

I've been using -90V fixed bias with an additional  -180 V bias generated from 2K of grid leak.  The specs call for about -200V for class C, but I found at -270V the tubes are off the scale for efficiency and no plate color.  The performance appears to be excellent for THD.

I just need to determine the best way to turn the finals on, etc., as mentioned in my last post.  That may be the easiest way to proceed and eliminate the LOUD clacking of step start contactors... :o

T

Tom,

Looking at Stefano's scheme, it seems that it should also work.  You're right about the relay noise.

I thought you said that without drive there is no current  or the current stops dead.  Wouldn't keying the drive on and off be enough to turn the finals on and off??

For the modulators you could just key the screen voltage on and off, leaving the plate voltage on.

OK FB on the bias, you never mentioned that you were already using some grid leak bias.  I didn't think -90V bias was enough to drive the tubes far enough into cut-off.  So, it's a total of -270V.

Fred

Yep, looks like a plan, Fred.

Somewhere back in this long thread I did mention I am running -270 v total fixed/grid leak bias, giving excellent efficiency.

The -90V is probably at about class B cutoff since I have 500V of screen on them.  I chose to make the -90V regulated to avoid RF rectification charging that has been a problem in other rigs.  The unreg fixed bias wud just creep up higher and higher during a transmission, needing more and more drive. Kinda a runaway thang.

So, I'm installing the the relays and resistor dampers now.  I think leaving the HV on with CTs grounded, while using RF drive to activate the RF final -  and screen voltage to key the modulators will work FB.

I may end up keying the RF screen voltage in the pri too, but not sure yet.

Want to add screen safety shutdown relays eventually.

Shud know maybe within a day how it all works out.

T

Tom

I keep all the voltages ON the RF and AF tubes always.

My winter evenings routine goes like this :
The RF tube is a tetrode and the AF tubes are triodes.
So I first turn on the RF blower and modulator funs, after all filaments with CTs permenantly grounded through the Amp meters that are fully protected, in the same time with filaments comes 30% safety bias to the Rf tube (-140v) and cutoff bias to the AF tubes (-200v) because the bias bleeder is ungrounded by a relay at this moment, there is of course a leak resistor for the rest 70% of RF bias (-300v for a total bias of -420v), after I turn on the 5500v RF plate voltage supply (6200v at this moment) with a 3 steps starter, 3 steps of 50ohm resistors in order to help HV capacitors' bank and modulation cap to be peacefully charged up through the modulation transformer (no idle plate current indicated yet), after I turn on the 4000v AF plate voltage from a different supply with an also 3 steps starter, on the end I turn on the 600v RF screen voltage slowly with a variac through screen protection circuit and self mod. choke (at this moment I get a very small indication of plate current about 10-15ma which is the condition with all voltages on and no excitation so no total bias). Now the system is ready for a long ionosphere riding. I leave it in the basement and go to my shack checking it from 2 wireless cameras (one to the Bird43 indication and one to the meters). I do these manually in about 15 min and only once in the begining of the evening. I of course come on the end of the evening to turn it off oposite way.
From the shack I move the rotary switch to the
pos1 and the ant relay moves to transmit,
pos2 and the RF exciter (rice box) turns on (44w) in this point I can see 70ma grid current, 180ma screen current and 1,6A plate current with the same order another relay grounds a 100ohm/200w tapped bleeder in order to set the modulator's bias at
-100v and its idle current at 80ma per tube (total 320ma),
pos3 and the 2 very important relays disactivate the 2 resistors from the chokes letting them free to play their modulating roles,
pos4 and the audio is on

When I turn off first audio goes off, then the relays are shorting the resistors to the chokes and make them relaxed, then the modulator's bias cuts it off and in the same time excitation can be easily off now because chokes are shorted by the resistors and have no energy for sparks and on the end the ant relay moves to receive.

As far you use tetrodes at the modulator keep the cathodes always grounded by filaments CTs and instead of altering the bias for cutting off the modulator, as I do with my triodes, in the sequence position 2 you could turn off the screen voltage from its ac side by a simple 220v/5A relay and you are set.

I was out of country for business and so I had not time for am phone otherwise I would  respond sooner.

Stefano

Put a poster of Marilyn Monroe up on the wall.

Stefano has a maul

Excellent, Stefano!

I follow your description clearly and will do a very similar set up here.   OK on ALL voltages staying on and the finals controlled by the fixed bias and also RF drive.  Also, the CTs are grounded all the time.

I will use the screen primary to control the modulator keying as you suggested.

The screen relay and resistor are already mounted and now working on the HV Heising relay/ resistor.  That is the key to taming this - the resistive dampers. Now the back-EMF will have somewhere to go and is rock solid.

I will use the contactors to set up an initial step-start that is used only to turn the HV supply on at the beginning of the session and stay on.  Right now I use the HV supply smoothing choke as the inrush softener, but that is really not enough.

The AMfone board should post your solution above in the archives, as it is a well thought out solution and I'll bet many guys building plate modulated rigs could use parts if not all of your suggestions.

BTW, you built  quite a FB transmitter with  5500 vdc  on the plates.... ;D   I seem to remember you posting some nice pictures a few years back. Could you post the latest pics of it?

73, and thanks again for the help, OM.

Tom, K1JJ

When I turn my rig on it ALWAYS returns the favour.

Dave, I'm not sure how we would ever get by on this forum without your invaluable advice.

Fred

Are you British now?

All the thanks to Stu...
He is the creator of this circuit and I just followed his instructions.
I had very serious problems on keying my transmitter, the same like you.
I was very desperade and had almost done all the tricks with sequencing, bypassing, relaying left right. I had also tried to turn off the driver by a potentiometer at its output voltage very slowly like a dimmer but as soon the exciting wattage went from few miliwats to zero I had thunders in the lab.......
Then I asked for help here and Stu cared to check my situation. The result was fantastic. Happy end.......

I'll be very busy for the summer and 90% out of home but I promise you to put many pictures from the new look transmitter as soon I am back for good. It will be a very interesting surprise for you Tom...
Wish you the best.

Stefano

OK Stefano -

Glad you got yours running so smoothly.

Yes, Stu has helped me out in a few areas too.  His advice is usually well thought out, as we'd expect from the college level engineering professor that he is.


Well, not wasting any time, here's a few pics of the screen 50 watt 5K resistor and vacuum relay installation. I left in the CT PTT relay as-is in case I need it again.


Notice I have the RF deck on a permanent Lazy Susan  for easy access to all parts.  The cabinet slides off in seconds. Same for the modulator cabinet, though it is on caster wheels instead.

T

And, here's the Heising choke 10K 200 watt resistor and vac relay installation. It's in the rear of the rig.

I'm glad it's almost finished cuz things are starting to get crowded... ;)

The cabinets are all built and painted IBM blue.    

Might make a few more mods and fire it up again tomorrow.

As an experiment, I'm going to try it with the new dampers using the original CT keying on both the final and modulator, just to see what happens. This will tell us just how good these dampers work.

T

You bloody wright, mate!
I apologise for being such an arse, but I practise at it, being off colour, I am.

What are you bloke, a bloody English teacher now?   ;)

Thom

I'm the last guy who should be an English teacher.

You'd figure it out somehow Fred and it would probably involve several transformers.

English can be corrected by a $10 / hour English major student.  You, my boy, should be writing for David Letterman.   ;D

T

Someone needs to write for Letterman. He ceased being funny about 20 years ago.

Well, the 60A contactors arrived and I couldn't resist building a HV step start with them. These are BIG mofo's and heavy. Much bigger than I thought.  Only $10 ea on eBay used. 20 watts each to key.  POW!


I ganged the three poles together and this makes a 180 amp  contactor.  I've always had problems with contactors sticking due to arcing, so this should solve it.  I use a 2 pole breaker to feed the contactors, so the 120-0-120 legs are totally disconnected when off.

The delay is about 3/4 seconds  before the second contactor comes on and shorts the 10 ohm 200 watt resistor.  (two 5 ohmers)

I'm using 24vdc contactors -  using 4 ohms and 30,000 ufd for the R/C delay to the second coil.  

Works like a charm on the bench.

The contactors are loud, so I 'm building a cover box that is lined with 1" of styro insulation. This will seal and keep things quiet, I'm hoping.  Notice the 1.5" border around the inside parts to the edge of the plate to allow for the styro..


The HV step start will work on both AM and ssb for the linears. I've always liked the idea of having the HV off when in receive for sanity reasons... ;)


I decided to change a few plans and key the HV and screen supplies.

The new PTT sequence will be:  (With final and modulator fil  CTs always grounded)

1) Ant relay on

2) RF drive on

3) HV step start on

4) Both screen supplies turned on at 120 primary transformers

5) Both RF screen choke and Heising resistor dampers lifted off

6)  Audio on


Unkey reverses the above sequence.

On unkey, I like the idea that the dampers come on immediately and stay on -  and the RF drive stays on until the end.  This should suck out any remaining back EMF.   The HV and screen supplies will ramp down since they are keyed at the primaries.

We'll have to see how it works. Received the 100 watt 1 ohm filament adjustment resistors today and also need to install the screen keying circuits.

T

New HV step-start keying 240 VAC primary:

step start with moose contactors .... sounds like social interaction up Timtrons way

I spent a bit of time and designed a digital sequencer .... this mimics a drum switch controller and is easily expandible as long as the control action resembles a push down stack .... many different ways to do this and may already be available off-the-shelf

if anyone is interested, let me know

Tom,

Whole set-up looks good.  I have contactors bigger than those for starting motors on some of my machines.

I see you're going with both methods, this should work FB.  If it doesn't, we're back at square one.  Try to keep the timing between the HV and screen supplies close.  You don't want no screen voltage to cut off the tubes before the HV has time to decay.  On start-up it doesn't matter but on shut-off it might.

Fred

PS;  if my lights dim down here in Jersey, I'll know things aren't going too well. ;D

It frickin works!!


After some more mods I finally fired up Fabio II. Tested to see if the new sequencing system stops this bad gap arcing when unkeyed.


Here is the final configuration -  when the PTT is hit:  (1 to 5)


1) Ant relay on

2) RF drive on

3) (Three at once) HV step start on, modulator screen supply on, RF final screen supply on. (ALL supplies keyed at AC primary)

4) (Two at once)  Heising choke resistor damper off.  RF final screen choke resistor damper off. (Using vacuum relays)

5)  Transmit audio on

Unkey, the sequence reverses  steps 5 to 1.


I'm still running just 2KV for now. Unlike before, there is no sign of arcing on any of the gaps during key or unkey.  I even tightened the gaps up quite a bit. All of the current meters are well behaved with rock-solid motion. The only minor aberration is that the modulator screen current moves up as it discharges the screen supply after unkey once the HV gets below the screen voltage. No problem. It's only about 50ma total - the tubes are rated at 280ma screen total.  

The HV drops off very quickly as desired.  I think the dampers are really doing an excellent job killing the EMF.  The sequence is maybe 3/4's second long.. not bad.

Next I'll run some more tests and then ramp up the HV to see what happens.

Another problem, but can be fixed:  The HV step start contactor is so loud it makes the rig hit 100% modulation  -  BANG!  It's like Fabio is shooting himself.  I'm going to find a cover for the contactors and line it with 1" of styro insulation.  

I just love the keyed HV. Nice feeling that there is no HV in the shack when unkeyed.


I didn't see any signs of instability in the RF final or modulator.  Think it's gonna turn out to be a FB rig.

Also working on a new 75M 2el wire Yagi at 140' high, facing Washington state WNW. Supported with two 36' long boom bridles, one for each tower to keep it evenly spaced and flat.  We on the east coast have been neglecting the 75M AM guys out west for too long and I want to get some new coast to coast action going soon.  W8, W9, W0, W7, W6, W5, etc.


THANKS to all who have lent their sequencing expertise. It made a big difference.

T

Keying the H.V. is much better than leaving it on.  Even with my old tube PWM rig, which used a 10,000V power supply, I keyed it on and off (with a step start).

Much safer, too!

Hopefully, I'll get to hear the rig on the air sometime soon.

Regards,

Steve

I thought you were going to unkey the screens ahead of the HV.  Although, I suggested keeping the timing of the two close.  You have the HV and screens keying and unkeying at the same time.  This shouldn't be a problem as I see it.  The screens will draw more current if the plate voltage is less than the screen voltage.  We had no way to estimate the decay time of the two supplies.  Seems the HV is decaying faster than the screen supply.  I don't think any of this is a problem.  Also, this situation may change when you increase the HV to the normal operating level.

I agree,  no reason to have the HV on when you're on receive.  No need to worry about HV lurking about when you're just in the listening mode.

All you need to do now is to reduce the contactor noise.  I see you're using two of the same contactors to step-start the HV.  The one that shorts out the 10ohm resistor could have been a smaller relay.  There shouldn't be that much current surge on that relay as most of the current is flowing in the resistor.

Anyway, glad you have it working.  I knew it would work FB.  If it didn't, I was out of ideas.  Having increased the time decay of the plate current dropout even a fraction of a second greatly reduce the back emf in the reactor.  Add in the snubbing resistors, it had to work.

Finally, add in what we all have learned with this thread.

Fred

Hi Fred,

I think the HV and screen supplies are so slow to ramp up or down that it wouldn't change anything to make them separately keyed.   Maybe lengthening out the sequencing steps would do the most to give them both more time to discharge before the ant relay drops out.   But right now I see no signs of power needing a place to go.  It keys just like a tame linear amplifier... ;D

I have only four steps to work with using this sequencing board, so that was the main reason to group some of the functions together.

In hindsight, I think the resistor dampers on the two chokes were the big breakthrough. I never heard of doing that before and I'll bet it wuda solved the problem even without the HV and screen keying, as well as keeping the CTs keyed.


Steve, I will be looking for a critical report when you hear it. I've already run some THD tests and it looks above average. There are distinct THD sweet spots when running various loading, screen voltage and drive levels - as well as modulator idle bias settings. The modulator seems be cleanest idling at about 200 ma, whereas higher idle gets worse, against conventional thinking.  I can see the distortion go up and down. When optimized, the thing seems to be pretty clean. It will probably get cleaner once I raise the voltage up some.   Fabio I didn't like 2KV very much and got better at higher voltage.  I have about 8dB of NFB dialed in and that seems to help extend the low end down to about 20HZ.  I can see the shark fins, just like the e-rig, so that's a good sign.

Looking forward to getting on 160M and 40M AM too... been a long time and I've made it easy to change bands with pre-sets and coax antennas.

See ya on soon!

T

nice going Tom .... sounds like a good solution ... I have finished initial design on a digital sequencer .... can be anything from 2 to 8 off-on-off steps using cheap and readily available LS parts ... this is a clocked design and allows changing step times to allow for relay activation speeds ... this has been fun and remininded of the kind of work was available before NAFTA ...73...John

Would that trick work with just a mod transformer as well, without a heising reactor?
What about the resistor value? Does that have to be in the final tube impedance range?

Martin

Hi John,

If I run into any more problems related to needing more sequencer steps or customized spacing between steps, I will take a look at your new development.  If I had known about it earlier, I wud have used it, but this 4-step unit is hardwired in and working for now...

Martin:   Yes, it wud work FB. There's no reason why the damper technique wouldn't work with a stand-alone mod xfmr. It's all about putting a load across the modulator iron, however it's done to dissipate the back EMF.

Stu suggested 5K which would be the impedance of a typical QRO RF final.  I used 10K simply cuz it's the value I had in 200W.  

Once I ramp up the voltage above 2KV, the real story will be told whether the rig stays glued together.  I bet it will be fine.

T

A proven sequencer.

http://www.w2drz.ramcoinc.com/Sequencers.htm

That's the exact sequencer I'm using.... ;D

BTW, I was up on the tower at 140' for 5 hours today. Some complications. Finally got the first 36' bridle up ready with ropes and pulleys for the new WNW wire Yagi.   Windy day. I'll tell ya, this work is unnerving and I'm beginning to dread going up there.

The rope and pulleys might be the way to go in the future to do most of the antenna changes from the ground... ;)

T  

For wire antennas, that's the way to go.  I only have to climb the tower if something goes wrong with a microwave link, or with the pulley itself (which is very rare).  Otherwise, I just lower the antenna and stay on the ground the whole time.  This is particularly useful during the winter months when it's 10 degrees out and windy and where climbing would be VERY uncomfortable or impossible  :P

thanks Steve .... I was not aware this board was available .... the one I designed is similar but different since I never met 2 digital/analog designers who did things the same way...   ;)

Lots of ways  to do it. A PIC could be used too and any set of delays and sequences could be programmed.

Tom,

At some point, if you feel like trying it,  I'm wondering how much of a reduction in the back emf was attributed to just the step-start of the supplies.  Meaning, the slower decay of the HV and screen supplies should have greatly reduced the voltage spikes from the two reactors.

You would have to not use (disconnect one lead) the snubbing resistors (just for a one time try) and keyon the rig and keyoff to see how much, if any, arcing may occur.

From the math, the voltage spike is directly related to the rate of change of current in the reactor.  The slower rate of current change caused by the slower decay of plate and screen voltage may be all that is needed to prevent the arcing.

Just wondering,

Fred

One of my amps has a snubber circuit on the HV. No arcing on key up/down.

Fred,

If I hadn't put so much work into this project I would probably try some experiments and disconnect the dampers, etc.  I'm curious as you are.

But, all of the techniques combined seem to be doing the job and the rig is very quiet and stable during keying. I wouldn't want to risk disabling the dampers. When I was experimenting with sequencing last week I had two instances of fireworks that broke some parts. So I shouldn't tempt fate again and maybe lose a mod xfmr next time... :)

The next risk is to raise the HV. That in itself is scary.   I'd rather risk parts doing that with all suppression working.

T

Tom,

OK FB,  If there's a chance of damaging parts I wouldn't try the test.  Like the old expression says, quit while you're ahead.

If anything is on the edge, you'll find out when you crank up the voltage.

Fred

Fabio II was running FB at 2KV with the new HV step start and damper system.  I then ramped the voltage up to 3KV.  It ran extremely well for about 5 minutes. Beautiful positive peaks.  Then BANG!!!! 

I saw an extended bunch of flames and arcs coming out of the back of the modulator. Please, not the mod xfmr!    There was an acidic smell in the air. 

After 30 minutes of conquer and divide trouble shooting, I isolated the problem to the Heising reactor.  Then I saw it - the new HV damper relay across the reactor was burnt and charcoal on its 24V coil.   It just can't take the abuse. It also took out the wire HV fuses in my HV supply.

Evidently there is a lot of energy still there even with the sequencing.

To make Fred happy, I tried the keying without the HV damper just to see what happens. There was a double arc, bigger than usual at the Heising reactor gaps.   I tried it again and this time shut off the HV supply and let the rig bleed it down before I unkeyed. No arc. Looks like I need to get that HV supply a longer time to bleed off.

Must order a new and bigger HV damper relay and try again.

T

Telephoto shot:  Today there were three hawks perched  at 190' for at least 5 hours holding court on 40M. Maybe they are making a nest / shack, I dunno...

The 2nd picture gives perspective.  The hawks are barely visible.

T

Here's the finished 36' bridle at 140' ready for the WNW wire Yagi.  Notice the ropes and pulleys ready to connect to the driven el and reflector. (Work from the ground)  

This was a bitch to get up there and rigged by myself.  The other bridle side will reside on the other tower about 50' below the hawks.

I just love wire antennas.


Third shot:   Yaz is showing his age, but still a good guy.  (10 years in August)

T

JA short path?

I was worried about the 24V line that close to such HV.  Didn't mention it cause I didn't know the limits of that relay.

You need to let the high voltage decay as slowly as possible.  Remember, it's only the HV filter caps that are discharging through whatever the load resistance is.  The greater the plate current at shutoff, the shorter the decay time.  The greater value of filter caps, the longer decay time.  You're already using big caps (100ufd).

Question,  Did the relay blow while you were testing or did it blow when you keyed off??

Nope, this is for the lonely 75M AMers in W9, W0 and W7-land we haven't talked with coast to coast in years... ;)  It will be facing about 290 degrees, Washington state.

Now that you mention it it will make a good JA short path, but that means I'd have to get up before dawn... gag gag.

T

Now that's funny!

It went when transmitting, which leads me to believe that maybe it started a path when unkeyed and then when I ramped up it just blew apart inside to the coil.  I may saw it in half to see what it looks like.   The bottom at the coil is melted but the whole case is intact.

I noticed that the HV damper resistor did get warm but not hot after many keys at 2KV.

Still thinking of what to change. 


T

Reading your comment again, you shut off the HV supplies before unkeying and there was no arcing, that's a good sign.  Seems that using the sequencer, it could be the drive is dropping out too soon, wereas there is still enough HV still present when the drive cutoff stops the current too suddenly.

If it blew while transmitting, then the problem has nothing to do with the back emf that occurs at keyoff.  The thing to remember is that under normal transmitting there is still very high voltages that occur at the reactor on voice peaks.

I think the relay you used is just not insulated enough for such high voltage.

The one thing you did prove out is that just shutting off the supplies greatly reduced the voltage spike to where you had no arcs.  Just what I thought would happened.

I think you should increase time between HV shutoff and drive shutoff.  That 100uf cap may be holding the charge a bit longer than you figured.  Another thing, maybe a smaller filter cap may be helpful.  Maybe only 30-50ufd.

I use 30ufd in my HV supply and a 50hy Heising reactor, I never had any arcing problems.

Fred

Fred,

The back EMF may have started the carbon trail before - then when I ramped up to 3KV, it blew when transmitting. Hard to say. 

Yeah, looking at the relay that blew, the coil has a long metal cover that extends to near the HV contact arms. It is not visible inside, but appears not rated for the job, even though it says 15KV.  I had that feeling when I installed it - it is only 1" tall, tiny, really.  The same relay in the screen damper seems OK.

I ordered a used Jennings 20KV vac unit that is 3" tall and obviously better suited. I think the guy will give me a credit on the bad one.

As for the sequencing... my sequencer  has fixed intervals and the order is the same in unkey and key but reversed.  If I slow down the overall sequence, it is too slow.   I might need something that will let me put a long delay in the HV position and also turn the HV on as a 1st or second step and drop out as a first step.  That wud give it more time do discharge it.

I'm going to keep 100 uf in the supply. I use it for the linear amps and want the regulation.  I shud be able to get it working at 100uf.

Despite whether the new relay will be able to hold up with the HV damper, it still concerns me that there was a huge arc when I unkeyed without the HV damper in place. I am not keying the CTs and have a damper on the screens. So, it comes down to the heisting reactor dumping power and HV supply timing.


T

You mentioned that the HV snubbing resistor was getting warm after many cycles.  It would cause it's damping the HV spike from the reactor.

You also found that letting the HV shutoff before unkeying you have no arcing.  Better to design the rig to have little or no back emf so you don't need to use the snubbing resistor.  At least that would be a target to try to hit.

We also know that dropping the drive causes a sudden drop in plate current.  The fact that you were getting some heat in the snubbing resistor tells you that the drive was causing the problem while there was still enough HV left to still have current flowing when the drive drops out.

You proved that shutting the HV before unkeying created no arcs.  Only thing left after that is to drop the drive and antenna.

Seems to me, you need to increase the time between the HV shutoff and the drive shutoff.  This way the HV has more time to decay down to nothing or a very low value before the drive drops.

Fred

OK FB on the timing not being adjustable between steps.  No sure what to do, not sure what exactly drops the drive, a separate relay controlling the driver or what?  If it's a DC relay that is keyed by the sequencer and the relay controls the driver, maybe try adding a cap on the relay coil to delay it opening.

Having said all of these great ideas, I think you should go with the better relay you ordered and use the snubber to cover all bases.

Trying to fine tune the timing may be too difficult to achieve perfectly and you know that the snubber was working great until the relay failed.

Fred

Some good ideas, Fred.

Well, here's what I've come up with...

I need a sequencer that will let me go forward or backward in a different order. Also the ability to change the time between steps wud be nice, but not mandatory.


The desired KEY-UP:

(Dampers are already resting ON)

1) HV ON   Screen ON   (HV Step-start on early will keep clacking noise out of key-up audio)

(no plate or screen current yet due to fixed grid bias)

2) Ant On

3) RF drive ON

4)  Both Dampers OFF

5) Audio ON



Un-key

1) Audio off   - Both Dampers ON

2) HV off   -  screens off

3)  Long Space or no assignment

4)  RF drive off

5)  Antenna relay off


Notice the HV and screen needs to key-on early -  and then un-key early.

It all makes sense to me doing it this way. However, I need a different sequencer to do it.

T

Those two sequences look good.  Having the HV turn-on ahead of the antenna shouldn't be a problem as without drive there wouldn't be any output.

The only thing I don't understand is why the plate current stops dead when the drive drops.  I would think the plate current would rise without drive.  If I shut off the drive on my rig the plate current increases.  To prevent that I use a 6Y6 clamp tube on the screen voltage.  The 6Y6 is controlled by the neg. grid leak voltage.

Not sure why your rig does the opposite.

F

This thread has been most interesting. I'm curious though, was the class E rigs flame out more/less scary than FabioII's? For sure, silicon does not recover easily after a flameout.

A good read on the use of a smaller reactor:

http://www.vias.org/eltransformers/lee_electronic_transformers_07_09.html

If I follow the article linked above, using Heising cap and reactor as parts of a high pass filter, can be done using much smaller cap (more Xc), and smaller reactor (less Xl), and yet still get 30hz to 10Khz response. The voltage transient issue would also be less extreme.

Jim
WD5JKO

Good read.
So if this was a seminal and industry changing article in the late thirties , would not most of the designs and BC transmitters constructed since then have the PI net, lighter weight components already installed?  Are not all the RCA's , Gates, etc. and our copies thereof already incorporating the PI AF filter method.?

Tom, sorry about your zorch.  Man, you are buying some high class replacement components.  Speaking of designs;
How are the high power short wave xmitter boys sequencing their stuff?  Harris n'gang.

let me think about this .....

Tom,

Thought about my last question.  You're using -90V fixed bias, which probably is enough to bring the plate current down to a very low amount, I remember class B level.  What you need is for the finals to pull more current with no drive.

If you can, reduce the fixed bias to a less neg amount (use more grid leak bias if needed) so as to allow the finals to draw current (with no drive) which is closer to the normal operating current.  I think you're running about 400ma during operation.  This way with no drive the finals will bring down the supply at a constant rate just as if you still had drive.  You already did this somewhat when you manually shut off the HV before you unkeyed and you had no arc.

This test may be worth a try.  You can do this with the same sequencing arrangement you're using now.

The thing to remember is that even with 500 volts left in the supply you'll still get an arc when the drive drops out because of the sudden drop in current to the class B level.  It's that sudden change in current that's causing the problem.

The screens only run 500 volts and you were getting arcing in that circuit before you made the improvements.  With that big Heising reactor you wud probably get some arcing even with lower voltages.

Fred

Tom,

If the HV damper became hot means that the reactor's relay often blocked in the "off position" and part of the modulation energy passed to the ground through the damper and the HV bleeders. From the kind of failure seems that your relay was very week and couldn't follow the on-off orders.
My HV is 5500v under load and I use a big Jennings for 15KV, 26.5v coil, never had a problem with hot resistor or relay coil failure.
When you'll feel secure with on-off by using dampers you will realize that keeping all voltages on during receiving is not at all dangerous as soon you use 2 basic protections.

First protection is the RF amp's screen overcurrent relay that cares if you loose RF hv, in this case this relay disactivates the RF amp's screen voltage and the modulator's screen voltage, too (cutting primaries).

Second protection is the RF amp's safety bias setting which must be so that in case of loosing excitation the RF amp stays idle at 10-50ma which in my case was many times my good angel and as Fred mentioned earlier will keep the reactor not to dive suddenly to the no current/huge voltage situation.

2 protections, one bias setting and one current relay let me keep voltages always on and on-offing as fast as the linears do...

However step start and voltages on-off make things simple but considerably slow,
2-5 secs is a safe time for using this way.
In this case you don't even need the dampers and the sequence is simle like this :

                            
                                 ON and oposite OFF

1)ant relay to tr
2)exciter on
....1 sec delay....or 3 empty clicks in the rotary switch
3)RF hv and screen on (step start ac)
....1 sec delay...or 3 empty clicks in the rotary switch
4)Modulator hv and screen on (step start ac)
5)audio on

A 12position 1pole rotary switch with the 1st or 12th position connected to a huge "on air" is the key for all traditional amers here in Greece....

Stefano

Great info, thanks.

I checked the screen damper relay that had its coil in PARALLEL with the blown HV damper - it was OK. So was the sequencer relay controlling them. I'm amazed that the HV relay melted down its coil but the screen relay was untouched.

Fred, yes, I have -90 fixed safety bias and about -200V grid leak.  I am trying to find a smaller 50w zener diode for say, 30 to 50 volts so I get SOME plate and screen current idle. Right now -90V fixed just cuts it off. Having that small idle would stabilize things more during bleed off.  Seems DigiKey and Mouser do not carry them anymore, or maybe I missed it. I want the stud mount type.

Stefano - OK on the sequencing and rotary switch.  We use fast break-in here, so need the PTT.  I'm finding about 3/4 second for the HV step-start is about right to bring it up to 3KV. If I activate the HV step-start first, it will be ready by the time the other functions key up.  I plan on screen overcurrent relays soon. I have them in all my tetrode linears and they have saved me many times.

Jim, I've had my share of class E rig shutdowns during initial testing, but the shutdown board worked well. I usually like to shake down a rig by putting it thru its paces and ramping it up, expecting to break parts. It then becomes a reliable rig once shaken down. I just feel more comfortable breaking parts in a tube rig rather than a solid state rig. Troubleshooting is easier for me there. There probably isn't a big difference in flashover reliability once they both are working as designed.

John / BFS:  I think your experimental sequencer might be my next try if it is not too complex.   Is this something that you made a board for or is it a kit?

I did look into Bruce / XR's suggestion to use the NCC timer relays. I am not sure if they can do a reverse order different than forward like I need.

Look at the "Timer Delay Relays"
http://www.nationalcontrols.com/products/productcategory.cfm?ProductCategory_Id=4307&Product_ID=1323#Prod1323

Maybe a string of these wud work.


I think Fabio II is very close to a working rig now - just need to get over the hump of these timing issues.  The audio peaks certainly looked impressive on the scope running at 3KV before it puked.


T

OK FB, I thought you were using a bias PS.  Since you're using a zener I guess it's in the cathode circuit.

I don't have a plate current vs grid voltage graph for the 4-1000 so I don't know what grid voltage to use.

Any way you can build up a neg bias supply and use it instead of the zener.  You should be able to add it in right at the grid meter.  Although, I'm not exactly sure what your circuits look like.

You can do this just for testing purposes and then go back to the zener if you can find them.  As for zeners, you can use a string of them, lower voltage and wattage using more than just one big zener.

Fred,

I'm using a standard bias supply applied to the grid, but regulating it by a 50 watt  -90V zener.  I just found some zeners at Newark and ordered a 62V, 33V, 24V.  Some combination should give the RF amplifier some idle when the drive is off.

I use a zener for the fixed grid bias cuz without it the RF drive will sometimes rectify and charge up this bias line and cause the bias to get higher and higher until it's too hard to drive.


I took the burned relay apart. Strange, even though it had been arcing and didn't click anymore, inside there was no noticeable signs of damage or arcing.  The coil was still good as well as the main contacts.  But the bottom at the 24V pins was all black.  It's like the HV contacts were arcing to the negative lead of the 24V.  The polarity EMF diode was shorted across the 24V pins.

I guess the new relay will work FB, being three times the size and all glass.

Still wondering what to do about the sequencer. Maybe John's design will fit the bill.  Making it go backwards in a different order seems to be the challenge.

T

"  I took the burned relay apart. Strange, even though it had been arcing and didn't click anymore, inside there was no noticeable signs of damage or arcing.  The coil was still good as well as the main contacts.  But the bottom at the 24V pins was all black.  It's like the HV contacts were arcing to the negative lead of the 24V.  The polarity EMF diode was shorted across the 24V pins.  "

Could it be Satan?


klc

Tom,

OK FB on everything.

I think you're getting close to having the rig work correctly even though you may not think so.  I hoping that an increase in idle current may be the final answer.  The sequencer you're using should work with the way you have it set up.

I'm trying to guesstimate what idle current you should try to use. Figure what your operating current is, I'm thinking 300-400ma (at 3KV 300ma = 900W input). I would guess that the plate current, at the exact instant the drive drops, is maybe half the operating current (just a estimate).

Meaning, from the time the HV is shut off to the time the drive drops, the plate current has maybe decayed to half.  So, if you set the idle current to about the same, when the drive drops out the plate current will still be about the same.  The HV PS and the Heising reactor will never know the difference (provided you don't spill the beans and tell them).

F

I am going to be busy at church for next couple of days ... we cook a meal for our shut-ins

I think Stephano and you Tom are right about the relay .... probably a partial loss of vacuum .... when you get the new one see iffin you can hi-pot test it to at least 8kv peak or so

I think I can get a sequencer to do what you need .... these only exist as a design ....I don't have time to lay out boards .... I was going to use a prototype board for my gpt-750 redo

Dear Father of the Fabio's,

The ultimate sequencing (using the time delays mentioned by Bruce)-

Take 4 time sequenced 'delay on make' relays for transmit 'on' sequence, through a 12 or 24 volt latching relay(s).. Set sequence to "Electron Wrangler" standards..

Take 4 parallel 'delay on break' relays  (now in circuit by the latching relay(s) being thrown), and set 'Un-Key' sequence  to "Electron King" standards..

On "un-key" the latching relay(s) comes home to start the day all over again..

It should work.. you throw the details together..  At LEAST use it in Fabio III

It's nice to have Sequence Freedom  ;)

Interesting, Jessie.

Look at the "Time Delay Relays"

http://www.nationalcontrols.com/products/productcategory.cfm?ProductCategory_Id=4307&Product_ID=1323#Prod1323

Which relays would you suggest for the job?  These are the NCC ones I think Bruce uses.


So we would be using four relays for make and four different relays for break.

I'll have to draw this out and see if I can make it work on paper.  Thinking more, I definitely need a sequencer that will reverse in different order to get the HV on early and turn it off early. This will give the HV a longer time to decay and also clack it's brains out before the audio goes on.  


TNX, OM.


John,  I'll look to see what you come up with. If I go with the Electronic Wrangler idea, I will let ya know.

Thangs happen very fast in OZ.


T

Bruce specifically mentioned the ones with the dip switch (numerical) set control as opposed to the pot.. I would contact him directly (sure you will anyway).. The cool part is 120 volts for make and break rails, through a latch.. Simple Wrangler Techno.. 


 at work, so I will give it more thought probably while caught in traffic later..

J

OK Jessie -

I drew up a schematic of a timer-based sequencer, but although it may work, I feel it may be a little Rube Goldberg-ish.  Could you draw up something of the basic design? I don't see how the latching relays are needed or how the relays work together and independently very clearly.

What is the difference between a make and break timer?  Can't we just use a standard make timer and use the other set of NC contacts?  I must be missing something overall.

I sent a PM to Bruce for his schematic, but haven't heard back yet.

This appears the best way to go with full control as you said.  Might as well build it custom for the job, caw mawn.


Tnx.


T

Hmmm...  Take a look at these delay timers for only $3.61 each.  I wonder if they could be used in a group of ten to give five steps of the desired sequencing forward and backward in any order?


http://www.ebay.com/itm/DC-12V-Delay-Timer-Switch-Adjustable-Module-0-to-10-Second-w-NE555-Oscillator-/230964055573?pt=LH_DefaultDomain_0&hash=item35c687ce15#shId
 (http://www.ebay.com/itm/DC-12V-Delay-Timer-Switch-Adjustable-Module-0-to-10-Second-w-NE555-Oscillator-/230964055573?pt=LH_DefaultDomain_0&hash=item35c687ce15#shId)

The NCC relays are very expensive and maybe these Hong Konks can do the trick instead.

Anyone have a circuit?

T

T,

Yes, Rube would be proud! (it's the thought that counts, right?)  ???
Thought about this some more..  All this is the raw brute force approach to sequencing..  It's the "Switch and Command Sequencer" caw mawn..

The point is you require a different sequence for key-up and un-key, simple right? **NOT**

*(These NCC timers are all available in specific time ranges and voltage  ..you'll find the range you want, and most are available on E-bay.. I used 120 Volts as a reference!)

Let's take 8 standard say DPDT 120 volt relays ..  4 for the Key up side (left)  , 4 for the un-key side (right) and lay them side by side .. Line up (4) Q1T series "delay on make" next to the left side and (4) Q3T series "delay on break" to the right.. Parallel all relay poles (left side to right side) except for one (see below)..

1: To sequence the key-up (left side) apply 120 volts to the RELAYS (the load) through the (4) Q1T-Series timers (delay on make) set to your requirements..   OK on key-up sequence.. simple stupid so far!

The trick is the LAST RELAY in your key-up sequence..
2: Use an unused pole of that relay to switch the un-key side (right) into the act by closing the "start" switches on the (4) Q3T series "delay on break" timers all connected to your right side (un-key) relays. Remember, the right side timers will have 120 volts applied full time (see PDF Q3T), and you will only be closing the start switches..  The right side relays are in parallel and they will be closed only after your last key-up sequence..  No latching required!  Then, the right side is in "control and command" because when you unkey (remove 120 volts from the left side and De-energize the relays and start switch) the right side stays energized for as long as you want ("delay on break") and release in whatever sequence needed..

I just got home (it's 3 in da morning -Tornado news coverage)  so I will make a drawing up in the next few days..

http://new.ametek.com/content-manager/files/NCC//Q1T-Series-Series-Load.pdf           (key -up delay on make)
http://new.ametek.com/content-manager/files/NCC//Q3T-Series.pdf                                (un-key delay on break)

PS. I use the Q3T with my "Johnson-Gates 500" through relays to delay on break the antenna relay and RF drive (transceiver used as a vfo) and it is VERY reliable..

Just saw your last post.. they would work.. do they make delay on break ones too? Anyway, the theory above should work. It really is the Land of Oz..  I'm off to dream about relays and sleep  :o

Hi Jessie,

I appreciate the explanation.  

I'll start looking for the timers and see if I can accumulate five make and five break.

Please post the schematic when you can.

After drawing out some other ideas while trying to use the Hong Konk timers, I gave up on it. The next step wud be a digital controller of some kind.  Your idea seems to be the only practical way to get the reverse order changed.  There are great advantages to being able to do this.  Lots of relays and timers, though...

Tnx, OM.

T

**UPDATE:  I found three NCC break-delay and four make-delay NCC   .05 - 1 second  120VAC timers at good used prices.

Also found a lot of ten  DPDT 120VAC standard relays at a great used price.

So maybe I can find the remaining timers soon.  I want five-five total.   Interesting that this whole system runs on 120V.   No big deal cuz it will interface to the outside whirl using floating relay contacts.

Great on the used timers.. I am sure there are more elegant ways to do the sequencing digitally .. BUT this gives you sequencing and individual timing on ALL
keyed events..
Get that schematic to you soon.. more tornado coverage OM ..

A toast to FABIO #2 ( and to this LONG thread)..

Jessie,

Yeah, this seems like the way to go... to be able to set the delay between individual steps to any value - and have the unkey sequence different from the key-up. Well tailored to the rig.  I remember Bruce describing this system before, but it really didn't sink in to the versatility it held. That's until I needed more flexibility and was locked into the 4-step standard sequencer. Now I see.

Among other things, this will allow me to key the HV immediately and the contactor step start clack-clack will be over by the time the audio comes up. Then I can turn the HV off first and give it the whole unkey cycle to bleed off as much as possible, using a long step. No way to do this with the old sequencer.

BTW, I was checking out your AM audio recordings in the link of the various guys.
http://www.dealamerica.com
Good editing and samples of their shticks.


Yep, this thread is long and if like similar ones (Fabio I, Rico Suave, etc) will probably go semi-viral over the next few years from Google people searching for info we have discussed.  It's amazing how many times I've searched for ham technical info on Google and got pointed to this website.  

OK on the tornado coverage. As a senior-anchor, I'm sure you are doing a  hi hi FB ham job at it. ;D

T

** Update - Found the remaining relays I needed on eBay.  Should all be here by the end of the week.  

Tom,

Main thing to do is raise up the idle current (no drive) to some amount (100-200ma).  I'm nearly positive this will eliminate the arcing.  I'll have to eat my hat if it doesn't (good thing I don't have any hats).  

You should be able to test this without the HV damping resistor.  It'll be good to know that the rig is not producing arcs and then add in the damping resistor for secondary backup.

You can run the test at 2KV, then if it looks OK try the 3KV.  If it's going to work, it will work with the sequencer you're using.

OK on the 5 step sequencer, I see you're trying to get rid of the HV relay noise out of the audio.  I guess the noise is still ringing a bit when the audio comes on.

You probably could have used some smaller less noisy relays, although I'm not sure how big your plate xfmr is.  The relay that shorts out the 10ohm resistor doesn't have to be as big as the main relay.

Fred

Fred,

I may be able to run some tests when I install the new zener - which should arrive tmw.

Just got the new vacuum relay today, but don't expect to risk it until I get a good working sequencer.

I actually DID try the higher idling current using a lower fixed bias back a few weeks ago. This was when I was still keying the CTs, etc.  It did not stop the arcing, but it may be a different situation now.  

With Fabio I, the higher idle solved the arcing problem, so that's what was confusing.

Anyway, with all the new additions going in soon, that back-EMF will have nowhere to hide.

The contactor clack-clack was in the key up audio simply cuz I was forced to turn it on late.  Then on unkey, it would turn off early as desired.  The new sequencer will allow me to have it fully completed by the time the audio comes on. I built a "sound-proof" enclosure for it, but it can still be heard, though less. With the new system, there will be complete silence on key-up and unkey going out over the air.


Jeff:  I see they shipped most of the relays for the sequencer. I'm having trouble visualizing the circuit that controls the un-key,  the delay on break timers and relays. Hopefully your schematic will clear it up.

T

Not confusing at all.  You raised the idle current but that didn't help simple because you were still opening the CT which instantly cut off all current, resulting in the same arcing.

Now you're no longer opening CTs which allows the finals to continue conducting current.  So, when you drop the drive the finals will still continue conducting the idle current which will finish decaying away the last bit of current.  If the idle current is very close to the plate current (with drive) at the instant the drive drops there would be nearly no sudden change in current (up or down).  It would be difficult to hit that target.  Not exactly sure how close it has to be, but 100-200ma is a good starting point.

As for Fabio I,  I didn't follow that threat so not sure how it was set up to operate.  If you were using the CT opening method and you raised the idle current to eliminate arcing, well hard to say why it may have worked.  There may have been some other conditions existing in that rig that are not in Fabio II.

Fred

Fred,

Fabio I used CT keying - that's why it's confusing that the higher idle worked.  But it added a  plate current surge upwards and dropped off before the RF drive dropped, thus the success of more bleed-off.   Seems last week I tried higher idle with the CT always on and the arc was still bad, so who knows until I get the complete system working together the way it should.


Jeff:  I drew out the circuit and  got an idea how it shud work. However, I wonder what will happen at initial power up?  Do I need to turn the sequencer on first, let it set itself and then activate the rig T/R system?  Hopefully it needs just one  initialization.

Also, Bruce mentioned in his old post that he used some of the relay contacts to make sure that each relay turned on before the next relay. Kind of a fail-safe.  Maybe we can add  that to the design.  There are two sets of  SPDT contacts for each relay available.

T

T,

One shot is all it should take.. when you switch in 120 though all 5 key-up timers to --->5 key-up relays it all happens at the zoo.. You will use the poles on those key-up relays in a sequence to trigger all events.. Just to clarify the second set of 5 timers (un-key) and 5 relays (all poles in parallel with the other 5) are there to keep closure on un-key for a different sequence..

To daisy-chain a fail-safe would be an exercise..  :P
at work again.. later

J,

Gots it pretty well figgered out now, tnx.

I just built up a chassis, front/back panels and drilled all the holes for the sequencer.  When the parts arrive we will be in business again.


Note to readers:    Jeff and I will take the new sequencer discussion off-board for a while.  I will post back with pictures of a completed and working unit - and a schematic for those interested.  The Fabio II project will continue from there.

Tnx for the help, guys.

T

It may not be done, but it sure is fun!

This is the new sequencer using delay timers to control both interval length and forward and backwards order. Full versatility to sequence the various relays in Fabio II. Five steps forward, five steps back, any order, any length.

Each LED will light up (1 of 10) to indicate which relay is activated. I left some extra jacks for expansion.

Everything found on eBay, cheap.

Lots of wiring to do before operational.  This and the four overload trip Hall effect sensor boards is all that's needed to get Fabio II on the air.  (When will it end?)


T

What kind of modulation transformer do you use that can take such voltages reliably?

Have you ever had issues with RF getting to the solid state relays and making them act crazy? Or is it as simple as a closed box and maybe bypass caps on each relay?

I haven't wired it up yet.

Though I know that Bruce / W2XR uses the same timers and circuit, but have never seen a schematic of it to know how it's bypassed, if at all.

It would be smart to use bypassing for sure - and place it all in a sealed RF-proof box.

It certainly is a big project just for a sequencer, but I had no other choice to get a variable ordered sequence.

Jeff/ W2NBC did the design on this one. Not sure if he is using one or not. We will post his schematic once it is tested.

T

An update:

I haven't forgotten this thread - just ploughing through modifications and testing.

The 5-step W2NBC sequencer works very FB now. The sequencer has gotten very complex with hundreds of internal connections, but the 4X1 rig now is as silent as a mouse. No arcing and it bleeds off the grid, screen and plate energy nicely.

At this point I have not bypassed anything in the sequencer for RF. It is running out of the cabinet exposed to the final. No signs of the solid state timers and associated circuits being affected.  The only thang that may need more bypassing is the solid state MOSFET driver.

Been working on optimizing the plate tanks for 160, 75 and 40M.  Had to add another coil and some C2 load padding for 160M. Now full output on these bands with a good Q.

Added a tiny 30 pF  17KV  vacuum variable neutralizing capacitor. The neutralization works FB and the feed thru signal sucked right out.  Very stable  on all bands of interest. (160 - 40)

Working on six optical-isolator sensors for overload shut-down  -  grid, screen and plate current of the RF deck and modulator. If any circuit exceeds a pre-set point, the PTT will toggle off and the sequencer will shut everything down orderly. (not counting smoke and fire)

Due to circuit losses, etc., the 4X1s need about 40 watts of drive total.  I am running them deep into class C which makes them even harder to drive, but more efficient.  I'm working on putting in a one MOSFET pre-driver that will take a few watts from the ricebox to drive the 4X1.

With the new sequencer installed, I brought the HV up to 3200V with no problems. This is the minimum voltage Eimac recommends in their datasheet, and that will be my high-tap.

The PTT key-up and unkey is dead quiet on the air due to the audio coming on last for  key-up  - and audio dropping off first on unkey. We hear just a carrier with no pops, relay clacks or thumps on PTT.

W2NBC did a recording the other night and it's getting there. Needs some more work.  Have a slight problem with low freq oscillation in the SS driver, but working on it.

The THD tests are encouraging.  At 100% modulation, I see the 2nd AUDIO harmonic down about -25 dB and the 3rd and higher drop off better than -40 DB++ .  Very sharp containment of energy up the band.   This is cleaner than my e-rig by 10-15dB in some cases.  The audio negative feedback made a difference as well as adjusting certain parameters to find their THD sweet spots.

I would love to set up a trapezoid on the scope, but so far have had no success. More later.


T

Here's Fabio II live at 2200 volts - the W2NBC recording last Saturday off his R-390:   The modulators  get somewhat cleaner at 3200 V.  Considering my average voice, I am pleased so far.  Notice the subtle lip smacks and breathing - and other high frequency sounds that require a good high end. Still needs low level processing, but is getting cleaner.

Shark Fins  ;D ;D  The acid test.  Seriously, it sounded pretty good the one time I heard you on.

I have the new big rig set up at Rattlesnake Island.  Look for you over the weekend if you're on.  I may have a mod monitor set up on the receiver - depends on how much tinkering time I have when I'm up there.  If I get it set up, I'll send you a transcript like I did one other time if you're on.

Tom,

You didn't mention in your update what you did to eliminate the arcing problems.

Are you using the damping resistors??  Did you increase the idle current (no drive) on the finals??

I'm wondering if my idea of increased idle current worked, without the damping resistors, to clear up the arcing issues.  Don't know if you tried it without the resistors.

Fred

Steve,

Well, I am seeing what I'd call "semi-shark fins."    The low end falls apart below 25 Hz, so it's not a bad compromise.  The SS driver uses coupling caps that limit it to about 20 Hz as well as the mod xfmr having its own limitations.  So all in all, I'm pleased with what I'm seeing so far.  I'll be interested to see what you think.

I've been hearing you on from Rat Is with the new rig.  Perfect audio, though sig down maybe 10dB from your closer MA QTH. Still rock crushing just the same.


Fred,

I haven't tried the rig with the dampers disconnected. Fear is the big reason... :-)   I did try it some time back with a small idle, using a lower RF fixed bias, and still had arcing.  So, the dampers appear to be making a big difference.

I still have the sequencer set slow,  at  3/4 second keyup and 3/4 second unkey.  The HV and screen supplies die off about 80% before releasing. This is a good thang until I speed up the sequencer and take a chance later on.

Today I had a BIG bang. The vac cap for neutralization was mounted 1" from the chassis and it arced over to chassis big time. Sustained blue flash. Took out the HV wire fuses and toasted the cap Plexiglas mount.  I re-mounted it 3" away from the chassis and it worked FB.

Had it on 160M using 3200V and everything hung in there very well.  I think the shakedown testing and perfection phase is going to take TWICE as long as it took to build the rig in the first place.  I keep finding new things to add or modify as it goes on.  

Gonna mount up a solid state RF driver tmw for 1 watt in, 50 watts out as an IPA. I'll be able to drive Fabio II directly with the one watt hi-tech SDR rig.


Itching to start on a new linear project - maybe a posse of convection-cooled 813's in tetrode config - not sure yet.  I need a quiet amp for those hot summer nights when Fabio II is just too hot to handle.


T

T

OK FB,  at 3200V, no sense not using the dampers for a fail safe.  You'll be able to tell how much the dampers are doing by the amount heat being dissipated by them.

Don't put your finger on them while the HV is on ;D  Not sure if you know enough not to do that ;D

Fred

After years of developing calluses on my tongue testing 9 volt batteries, why use my fingers?

T

Here's two pics of the finished 5-step sequencer.  All lights are on and all relays keyed.

It uses ten NCC timers and twelve DPDT relays. It will step forward and backwards in any order and also vary the delay between any step.

Works very FB now with Fabio II. There is no arcing or problems on key-up or key-down.

It's a lot of effort for a sequencing system, but the standard 4-step fixed step and interval did not do the job.

I left a few holes for expansion.  Still needs panel labels.

T

Here's the 2 watt in, 100 watt out  solid state amplifier used for a dead carrier - to drive Fabio II in class C.  It uses a CCI kit board using four MRF-150s.   It is rated at 600 watts out, so will be running conservatively.

It has a small fan blowing air thru the heatsink as well as across the copper spreader.  Seems pretty stable. There is a missing MRF-150 due to a previous mishap. Just ordered one from China for $26, free shipping.

It runs silently and will keep the load off my ricebox driver, needing only a few watts.   There is a 10A meter on the front for monitoring. The unit is rated at 50V - I am using just 24V.

There are no LP filters required since it will be driving a tuned grid and plate circuit in class C that will greatly reduce any harmonics.

Picture 2 shows a 3 dB resistor input pad towards the rear of the board.  I plan to add a shutdown overload circuit to the RF input in case of errors.

Still needs painting and labels.

This module goes after the antenna relay and feeds into a 50 ohm to 50 ohm unbalanced tuner which feeds the 4X1 grid circuit. Thus, this solid state IPA will always have a perfect 1:1 match to work into on the various bands.

As you can see, I take a modular approach to most all of my building. This is convenient when changes, additions or modifications are made.  Sub-systems can be reused without re-building all over again.

T

 Dang!.. there be some WIRES in there.. anyway, it works and that's a good thang OM.. Next time maybe a ribbon cable or 5 would make it " look" less complicated..  ;)
..and the amp looks great! A toast to Fabio and his offspring..

A neat ribbon cable?   Just wait til you see the rents I charge the local rats to live in there!


Yep, the NBC design worked FB.  The only problem I had is that the Q3T unkey timers did NOT want to be tied together and signalled with one set of contacts. I needed a separate pole for each timer.  (see the extra 4 pole relay glued to the top on the right?) The Q3T triggers are solid state based and did not like associating wid each other, caw mawn.   Otherwise, smooth sailing and I'm moving on to the next trial by fire.


T

Here's the finished panels for the W2NBC sequencer and the new 4X1 shutdown overload unit.

Notice the power resistors in the shutdown unit that sample the RF screen, RF plate, modulator screen and modulator plate currents.  Works like a charm! The series resistors are in the negative lead of the supply or fil CT - and about 1-3 ohms. Each feeds an optical-isolator board. This in turn feeds the relays and latching circuits. If any current exceeds a pre-determined level, the 4X1 PTT sequencer methodically unkeys the rig.  The iso boards and relays worked out FB and I may add these to other rigs.

The four holes are for fine-tune trip sensitivity pots to be added later.

I am using another method to shut down the RF grid and Mod grid circuits in case of overload. They involve shutting down the SS IPA.

I realize the wiring is not dressed off, but on certain units I sometimes leave it loose to make troubleshooting and servicing easy in the future. It is very difficult to trace out wires that are bound together.  This way I can usually fix something quickly without the schematic.

Now down to final testing and optimization of  Fabio II since all the safety devices are finally in place.

T

And the IPA. No name for it yet...

Fabio testing resumes.  More gadgets added. Everything still out-of-cabinet.  Black lettering on white, caw mawn.

It's really too hot to test, so I'm starting a new pair of grounded grid 4-1000As linear amp in the cool cellar workshop. Regulated screen and grid.  Check the QSO section for the next thread.


***  Here's the new 4-1000As linear project:

http://amfone.net/Amforum/index.php?topic=34543.0

T

Well, I finally got around to running some THD and IMD tests on Fabio II.  Had it on 160M last night and got some good audio reports. However, the THD test is what tells the story.

Running a single tone THD test while loaded up to full power, I'm seeing about -35dB down for the 2nd harmonic peak and about -45dB for the 3rd peak.  Some of the higher order peaks are down -50 to -55db to the noise floor.   It's actually cleaner than my modified FT-1000D on AM.  The heavy negative audio feedback certainly helps the THD. I'm real pleased considering it's a plate modulated rig with a mod transformer, phase shift, etc..

I found by playing with heavier loading and different screen voltage, I can dial in better numbers. This tweaking must be tailored to the individual rig. I've also found what works for some rigs, doesn't work for others.

Anyway, here's a screen capture off my HPSDR.

I plan to get Fabio II on 75M AM tonight, so check it out if you are around.

T

Here's some pics of Fabio II.  I still need to tidy up the cables and screw the cabinets on, but it's almost finished.  (and tested)    The enclosures, when unscrewed, slip off in seconds for full, easy access.

The first pic shows the RF deck that swivels on a pedestal for easy servicing.


In pic 3 see the solid state (WA1GFZ design) MOSFET audio driver and the MRF-150 IPA RF driver.

T

First pic is the new pair of 4X1s in linear with its cabinet on.  Its name is Rico Suave II.  GG with regulated screen and grid voltages.  Very clean amp and fast band changing.

The small accessory boxes in the second pic are an RF unbalanced to unbalanced input tuner, a six step variable sequencer and a failsafe shutdown system. The shutdown monitors 4X1 plate, screen and grid currents of both the RF and mod decks. If a preset threshold is exceeded, it will break the PTT line.  Works FB so far.

T

It appears Fabio is still in the shakedown mode. It had about seven on-air crapouts tonight.  There were severe flashovers and three Teflon PL-259s coaxial connectors burned up.   These symptoms are clues to the main problem - HV arcing to the antenna 50 ohm line!

At first I thought the burned PL-259s were from testing the rig in high tap. But after finding soot marks I found two problems.

The first one was plate cap parasitic suppressor placement. Even though the suppressors were about 1.5" from a grounded bracket, they still arced to the bracket.  The suppressors were melted. I added a Plexiglas shield over the bracket.

Tried again and the flashover repeated, but in a different spot. I blew out another PL-259 in the antenna line and all the wire fuses in the HV supply opened up.  I found some more soot. This time the top of the RF plate choke was arcing over to C2, the loading cap. It was about 2" away, but not enuff for RF I guess.  This 4KV + 4KV (8KV)  voltage was going through my antenna line, thus burning up the PL-259s.  I even smoked an SO-239 on the Bird wattmeter.   I guess the HV pulse wasn't totally squelched by the RF choke across the 50 ohm line.  This is a strapping choke wound with #20 wire. It is still good.

I noticed the small 2.5 mH RF choke across the 50 ohm antenna line, used for static discharge, was open. More evidence that there was HV there.  Cheez.

Anyway, I added a second Plexiglas shield to the plate choke and hopefully tomorrow will be a better testing day....  ;)     This plate modulated HV stuff can be squirrelly until isolation and spacing gets worked out. I've been through this before. Eventually the rig runs FB without arcing.

T

The new rig sounds good, I heard you last night after I got done talking up on 40 meters, you were troubleshooting the triple carrier problem you were having on 3875 when I heard it.

Thanks for the report, Shelby!


Yes, the FT-1000D driver has a strange birdie problem on 3875. It's in the design and puts out two additional carriers 2KHz above and below.  If we look at the spectrum picture in a few posts back, we see a peak on 3882 and 3878. They are down only -40dB on 3875 and can be heard as weak beat notes. But they are down -60dB when on 3880 as shown in the pic. Not sure if anything can be done with it since other FT-1000Ds do the same thing. Probably synthesizer design.  Might need a different driver when on 3875. I have an HPSDR that might work.

Hmmm.... I wonder if this is caused cuz I bypassed the AM TX filter? Seems like 2Khz is too close to make any difference though. Anyone else have a stock FT-1000D? Please put it on 3875 TX AM and listen on another receiver to see if there are weak carriers on 3873 and 3877...



It was a lively session last night with many coming and going...

T

Would you mind posting the schematic of the modulator including the feedback? It would be beneficial to anyone concerned with a clean signal.

Tom,
Make sure that the HV blocking cap from the top of the plate choke to the tank is up to the task.  The 2.5mH choke shouldn't have let go due to HV. Don't want HV on the ant feedline. Could make for a deadly situation.

BTW, nice looking and sounding rig.

It looks reeeeal purdy Tom! I didn't have any rigs on last night but noticed the southeastern sky was flashing so I suspected you might be operating. Looking forward to hearing how it all sounds.

Rob

Tom

My stock FT1000D also puts out a pair of sidebands +/-2kHz from the carrier in AM mode on 3875kHz. The sidebands are 40dB down from the carrier... independent of the carrier level (adjusted with the drive control). The sidebands are much lower at other nearby carrier frequencies, and their distance from the carrier also changes at other carrier frequencies. They are 60dB down and at about +/- 5 kHz when the carrier frequency is 3880kHz. They are 80dB down and at +/- 14kHz when the carrier frequency is 3885kHz. At 3870kHz, there appear to be some close in sidebands (approximately +/- 500Hz) about 60dB down from the carrier,

Nice rig!

Stu

Thanks for the info, Stu.  Looks like the 3875 carriers are normal for the 1000D.

Opcom, I didn't draw up a schematic yet, but will in the future.  The NFB is derived from a 5 meg (string of 180K 1 watt resistors) across one end of the mod transformer secondary to ground.  I tap off a 10K resistor that's in the string, at the bottom of the string into a capacitor for audio NFB. This low level (1 volt audio signal) gets fed back to the input stage of the MOSFET audio driver, thru a pot.

Bob, I think the coupling cap is OK. It's a big 15KV job and today after a few hours work I see no more signs of arcing in the rig. I'm sure my big RF choke across the 50 ohm ant line wud cause fuses to blow if so.

Rob, I might get on tonight, so maybe catch ya.

Early today I fired it up and found yet some more arc over problems.  The 160M and 75M tank coils were arcing to one another even though the terminals were spaced 2.5" apart. I added another Plexi shield. Now there is no arcing anywhere, even at full strap.  Finally.

The bad news is my Bird wattmeter SO-239 connector arced over again. It is weak and disfigured  from that HV arc last night. I cleaned the Teflon, ordered a new connector on eBay, and will have to run the rig in low to medium tap for now.

T

T,
Odd that the Bird took an HV hit. Is it HV or just very big RF? If it's HV and  there's no loading coil down the feedline or at the ant you'll have HV down the feedline especially if the 2.5mH choke is open. The fuse may not blow in that condition and if the cap is flaky. The cap being a 15 Kv cap doesn't mean it can't go south.  Don't want you to have an accident. I know you're diligent but please be careful OM.

Bob,

The arc that caused the problem was from the 4X1 plate cap to C2 loading cap.  There is both DC HV and RF high voltage there.   Evidently the 50 ohm safety choke bypassed the DC and blew the breakers, but the RF voltage present there was not bypassed to ground by the choke.  Thus, instead of a normal 500 V of RF on the 50 ohm line, there was probably 4KV.    I'm glad that C2 didn't get damaged.

This was a momentary flashover that has been fixed thru isolation.  But still the remnants of this 4KV RF pulse may rear its head in the form of weakened parts in the 50 ohm line - like the SO-239s that once zorched badly with carbon tracks, cannot be made to handle full power again.   I'll just have to weed them out over time.

T

Tom... I have found that the so-239s and the pl259s that are used on the smaller hardlines   (5/8---7/8") are very well made and can be easily adapted to standard coaxes by someone that is handy with a soldering gun  I found some high quality chassis mount So-239s and silver soldered a pin into it replace a fried connector on my bird..working good at strap so far...Gud LUK...hope to hear you....Steve

Tom,
it sounds like you have a good handle on the situation. I know I don't have to tell you to be careful. You're pretty knowledgeable.  Just wanted to make sure.

For noise in weird ducting:
If a perpendicular transition or flange in the airstream can't be avoided, some "DAP" caulk can be used to give a fillet or rounded profile to the joint or a corner if it is making noise. This worked well mating the intake snout of a 500CFM blower to a 2 LB coffee can. YMMV.

To maintain continuity -  the next related thread - please go to:

http://amfone.net/Amforum/index.php?topic=35856.0

There is discussion about testing and troubleshooting Fabio II to improve frequency response and cleanliness.

Chico?  just a thought.