The AM Forum

Hola,

The new 4-1000A linear amp saw first light tonight. Everything is wired and tested - except for a HV test and RF into the dummy load. I want to do that early in the day... :-)

The filaments, blower, TR, metering and input matching work FB.

As seen in the pics, I built a 'T' network to match 160 - 40M,  50 ohms to 12 ohms. (four tubes in GG parallel equals about 12 ohms input impedance.)

The amplifier has two Plexiglas front panels as well as a 23" X 25" Plexiglas side panel for viewing pleasure.

QuadZilla (As The Derb named it) uses vacuum variables for both the plate tuning and plate loading - with turns counters. It also uses plug-in coils, which I may change to a large rotary band switch later. The amplifier will be used for class A service and driven by four MRF-150 MosFets.

For more info and early pictures, check out the original thread:  http://amfone.net/Amforum/index.php?topic=18568.0

Enjoy the views!

Tom, K1JJ

More pics to come...

More Pics:

Notice the adjustable 50 ohm to 12 ohm T network with roller inductor.

That filament transformer is feeding 7.5V at 84 amps.

Both the fil xfmr and blower are on 240V variacs for full range adjustments.

This is one of the few rigs I've built were there's plenty of room left over to work on it... :-)

More QuadZilla under Plexiglas:

I tried real hard to keep the plate RF strapping as short as possible. It was difficult with an in-line layout. However, I think it worked out FB.  The only thing to do now is to FIRE IT UP into a dummy load to find out.

Early construction pics:

Shielding?  SHIELDING?  We don't need no Stinkin' shielding   ;)

Good thing Hams don't need FCC type acceptance for homebrew.  ;D

Why would shielding be needed?

Excellent Tom....!!

does it do 11 meters?

Shielding? Cable TV is shielded! Might be good to check the outpoot circuit for VHF resonances?

My single 4x1 produced an awesome event of releasing energy when the plate parasitic suppresor (5 parallel 2 watt resistors inside the small coil) eventually cooked... replaced with nichrome and a globar... now that suppresor could supress the VHF energy running at 6kv B+. 

kl7of,
Maybe a battle brewing here.  MODZILLA (aka Pauli Guhrl) vs quadzilla coast to coast Saturday night brawl.
woc

When you're in an old buzzard qso some night and you feel unusually warm you may rethink the shielding situation.

heheheheh...

Yep, I had hoped we'd get a rise outa this project!

Today we'll attempt firing up "QuadZirra" into the dummy load. (the Japanese pronunciation)   I'll probably use the 3kv supply and later stick 6kv to her and watch her scream like a stuck dinosaur.


Shielding?  I could always add some of that fine metal screening to the Plexiglas. I just may do that. Though, my other rigs under Plexi haven't caused any RF in the audio or similar problems.  When someone axes about BA radiation, I always refer to the group of OT's from the 20' and 30's who died around the same time, back about 15 years ago.  It was listed in the AWA periodical.... these guys were the pioneers of radio, working around 10's of KW with no shielding for years. Most lived into their mid to late 90's. If anything, it'll clean out the stray crabs... :-)

I'm a little concerned about the vhf parasitic suppressor resistors. I'm using nichrome wire for each tube, but the resistors are only 2 watts. I only have two 50 ohm glow bars, so need more. If there are no parasitics, then the resistors will be OK. Being GG and operating no higher than 7mhz, it'll probably be pretty stable, but ya never know til ya smell that smell.

Unlike the rest of the house, my shack is a little colder cuz there is no cellar below it. Quadzirra will help a lot until it warms up.

Updates to come.

T

Cool rig Tom!!  Now lets see.....if I can ever get going again on it....a pair of 6C21s modulated by a pair of 304TLs should make a little noise.  I believe I will call it Kahoona III.  (Kahoona II is a 4CX1000/4CX1500B leenyar).

73,  Jack, W9GT

DAM you're fast Tom,
From birth, just a chassis with tubes and a PC board, to a working ANIMAL.
You will have to give encoded text for the Bird Watts out with the 6KV supply.

Are you planning any harmonics in your future. This thing may be the final step toward sterilzation.

Fred

Tom,

you should cop some nichrome ribbon offa ebay. unless that wires big you're gonna se it go poof when you apply the coals to it. put some  heavy nichrome STRAP on them bad boyz....

HF is non-ionizing radiation. Take a look at the MPE limits. Even at a few feet, there is not enough radiation coming off the short leads in that transmitter to be anywhere near the limits. You'll do more damage using a cell phone than operating that transmitter.

Just finished the first sea trials with QuadZirra on 75M, into a dummy load.  I started slowly cuz of fear -  hooked up the smaller 3500V supply. Drove her with 20 watts of AM carrier from the FT-102 directly.

Plate current idle looks good. I swung the plate and input tuning caps all different ways and could see no instability.

I added the limited drive, tuned her up and she puked out about 2200 easy watts. (Bird watts into a 50 ohm Bird dummy load, caw mawn)
Pattern loooks clean on the scope, no signs of parasitics or oscillations of any kind.  The AM positive audio peaks flew off the screen - that's a good thang.

The input T network adjusted the 50 ohms from the FT-102 to the 12 ohms tube input to 1:1 - easy.

I see a problem with the third tube towards the rear. It shows much less color than the other three. Probably slightly soft. Gotta locate another tube. They're all pulls anyway.

Might hook up the big HV supply and then drive her with the MRF-150's MOSFET amp within a day or so.

Added some diodes in the fil CT for bias. At 3500V she idles at about 250 ma with NO diode bias in there. At higher plate voltage she will need some bias to idle down.

I'm pleased with the amplifier gain. As far as I can tell, it's about 13db, which is in line with what someone said in a recent thread for GG 4X1's. I'll make some more accurate measurements later.

All tube plate color pics are taken when putting out a 2200W carrier. (pep) This is about 30% efficiency (like class A) but would increase to about 65% with higher drive in class B.  I noticed with higher drive, the plate color stays the same while the power output goes up, as expected.

When compared against the total AC power taken from the mains with my plate modulated 4X1 X 833A's, it's really not a bad deal overall.

T

Mo pics:

Scope Yallo.

Awesome! Looks cool, sounds good. You got it all.

In the bird watts pic.....what is that smaller meter in the background measuring?  The ft 102? 
In the scope Yallo pic.....Is that the carrier pinching down to the baseline?  Hard to see any positive peaks   are you using a slow sweep? 

In my best Japanese accent, "Oh, you vely smalt man!"

Yes, the little Midland swr meter is drive from the FT-102 where I can adjust it for min swr into the 4X1's.  Right now it is uncalibrated and overdriven. Normally there is no reflected.

The scope is showing a low bass note and is expanded.  If I do a whistle, I can see 200%++ peaks, since it's a balanced modulator driving the amp.  Maybe I'll take a better scope shot of it using an audio tone and post later.

All tube plate color pics are taken when putting out a 2200W carrier. (pep) This is about 30% efficiency (like class A) but would increase to about 65% with higher drive in class B.  I noticed with higher drive, the plate color stays the same while the power output goes up, as expected.

In class B, when compared against the total AC power taken from the mains with my plate modulated 4X1 X 833A's, it's really not a bad deal overall. I'm really pleased with results so far.

If you get on this weekend, maybe we can make a first contact using QuadZirra and your Fred Flintsone rig, Steve.... :-)

T

I think you need more blower...

Can you 'splain "carrier. (pep)"?

Is that 2200W carrier with the ability to do 100% maululation on top of it
or
Is 2200W the PEP level under the present conditions, and you are testing it with a 2200W CW signal?

danke

Hola Frank-

Are you basing that on the tube's plate color or size of the blower?

I think you're right and it's easily curable.

I have a 240 Variac on the blower now and it's set to a low speed at 120V. I can easily increase it to a hurricane at 240V, but the air noise comes up too. Once I settle in on a power and voltage level, I'll adjust the air accordingly. It might mean not running as much audio compression as I usually like to do.

Also, remember that the amp is running close to class A at 30% eff with little drive.  If I drive it harder, the power out goes way up and the color stays pretty constant, probably approaching 65% eff.




Danke said:

"Can you 'splain "carrier. (pep)"?
Is that 2200W carrier with the ability to do 100% maululation on top of it

or Is 2200W the PEP level under the present conditions, and you are testing it with a 2200W CW signal?"

Hi Danke,

The latter is correct.

Just to clarify further, if you drive an amplifier to near saturation with a dead carrier, you can consider this the maximum power it will put out. This is also the peak envelope power "pep" of the amplifier. So, when running AM, we would decrease our carrier by 1/5 or so to give room for our voice peaks and asymetrical voices -  and let our audio peaks reach near the pep level.

When I mentioned carrier/ pep, it was shorthand for saying I didn't have any more drive available for the test, so that the max power I cud get out of the amp was 2200W full dead carrier which is also pep for that drive level. If I were to switch to AM, my AM carrier wud be about 450w with 2200w peak audio power out.

I later tried the amp with move drive and found it was capable of much more pep output with the same plate color (dissipation) using 3.5 KV.



T

Tom... Is it considered to be class A operation with the low (20 watt) drive and 30% efficiency and class B with the higher drive and 65% efficiency...without the bias changing....?  I see you have that thing idling at 250ma with no bias...What will change if you apply bias?  (Other than the idle current) If you put a bias supply in and apply the bias all the time vs bias during recieve (standby)only... What about grid leak?     I'm considering building a 2 holer.

Hi Steve,

Glad you axed, cuz I just got done with some extensive tests and settled on some operating parameters for now...

Well, actually, true class A is idling so that the entire 360 degrees of the drive signal stays above cut-off and conducts 100%.  I was probably more in AB cuz the plate current was swinging upwards, but the drive was so low that it acted like class A efficiency.   I think when the amp is driven harder, it draws grid current, so the efficiency goes up.  But you're correct, class is mostly predicated by idle current.

BTW, to unkey, just open the fil CT with a relay. Look at the Telsa 813 circuit. For this linear, the diodes are in the circuit all the time, RX and TX.

Anyway, here's what I came up with...  I'm talking about class AB2 now. Running the amp at 6kv was way too much voltage for AM operation. Maybe it wud be OK for ssb, but on AM the plate dissipation was exceeded too easily and it made just too much power... :-)  I found that running it at about 3500V was perfect. For four tubes, this gives a dull orange plate color, with an idle of about 300 ma. (about 75ma X 3500V = 262W per tube) Considering they are 1KW dissipation tubes, this is FB.  It makes plenty of power output at 3500V - plenty.. :-)

HUZman sent me some old IMD specs for the 3-500Z showing the IMD was much better at lower plate voltage, as low as 1500V. I know some guys think the opposite, but maybe a lower voltage is better. I will just make it up in current.  Real high voltage bugs me anyway.

Another thing I've been noticing for years and have talked to a few people about:  On AM, when adding a lot of bias to a linear, until the tubes go below cutoff (just below class B - barely into class C) the linear operates very well on AM. The AM carrier seems to bias the tube into conduction and operates linearly when modulated. But on ssb, there is severe cross-over distortion cuz the amp stays below cut-off until a loud voice peak comes thru.

To confirm this, I experimented with adding diodes in the CT of the fil xfmr as bias to class C, and see that the tube plates glow duller on AM (less power dissipated) with the higher bias. This is probably simulating a class C grid/screen modulated stage.  Anyway, I loaded it heavily, brought the amp down into B/C operation and it operates very, very nicely on AM. I think the efficiency is up around 65% on voice peaks, from what I can tell.

I tried driving it with the MOSFET MRF-150's and the power output was tremendous - and clean. So, I have a lot of choices here on AM - to run it class C, B or class A - with or without the MOSFet driver.

I don't think grid leak is necessary with this config - it is so much easier to use a string of diodes in the CT and short some out to change the idle level for different purposes. For example, to go on ssb, I wud just short them out and it wud idle at 300ma - perfect for ssb. In CW, let them run in class C.  The tones thru the amp are very clean as is, so I don't think grid leak wud help to linearize it any more on AM.

It needs a lot of air, but running it at a lower voltage and splitting the dissipation amongst many tubes helps quite a bit to quiet things down. I found when using a moderate amount of compreesion of AM, the amplifier (8' away) creates just a small amount on on-air blower noise. Quite acceptable. With no compression, there is no noticable on-air noise.

So, I'm a happy camper. This is one of the few projects that fired up right away and had no problems or crap outs. That's a rare event, trust me.. :-)

Tell me more about the two holer plans ??

T

Steve -

After thinking it over, I'm going to try biasing the tubes far into Class C for AM (using more dodes in the CT) and see if I can raise the carrier efficiency.  It will act much like a standard grid modulated class C "efficiency" amplifier.

Also, the more bias it has, the more drive is needed. So good thing I have the MOSFET driver amp. I figure the efficiency will be the equivalent to a standard grid driven class C amplifier with standard grid bias and screen voltage that gets modulated via an audio transformer connected in series with the grid and/or screen.  But this will be a GG class C amplifier that gets its grid and screen modulation thru the RF signal. Since both grids are grounded, it is a composite grid and screen modulation system.

The thing is in GG, usually the drive signal does not get modulated - and is added to the output. The result is it will not hit negative -100% modulation.  BUT in this case it WILL be modulated via the RF signal and added to the output power, so 100% negative is achievable.

The GG stage is also very stable compared to a grid driven amp.

BTW, you axed about grid leak bias...  in GG, you want to strap all grids/screens directly to ground with copper strap. Grid leak wud require a floating/bypassed ground, so is not as good for stability. Use the diodes instead - but you might try a grid bias test anyway just to see what it does.

I plan to add a rotary switch to be able to select (short out) any combination of diodes in the string to go from class C to AB.

This could be an interesting experiment. From initial tests, this could be a great way to have a band agile amplifier with reasonable efficency on AM while maintaining tremendous fidelity and positive peaks from the low level balanced modulator driver.

I'll let ya know how tests work out.

T

Tom...vERY INTERESTING....I have been experimenting with a single GG 4x1 using a relay to switch in grid leak on idle and ground the CT on xmit...I just acquired a fil trans that will lite two tubes so I want to try the duece...So far I have only used 4 KV  I am want to try some lower Voltages...  I really want the low distortion clean signal  LOUD AM amplifier that I can drive with the 102 for push to talk..
     Are you monitoring the grid current?  Have you meausured the voltage drop(s) on your bias diode string?  I like the input tuning T...  Heavy duty....

Steve,

Just to clarify, when I say, "idle" I mean the quiescent, no signal current, when the amp is keyed. To put the amp in standby on receive, just lift the CT off ground, as shown in the Tesla 813 amp schematic. No need for grid leak bias unless you want to experiment with it on transmit only. But, in GG, the screen/grid shud be strapped to hard chassis.  Use diodes only - for bias.

Good on the FT-102 driver - FB... also the fil xfmr to handle 42 amps... :-)

My grids are strapped directly to gnd, so I'm not monitoring grid currents. It doesn't really matter cuz there's nothing that can be done about them anyway in GG, as long as their ratings are not exceeded. The Eimac specs seem to say GG is OK on the grids when the tube is driven to max.

I will measure the diodes' voltage tmw. I have about 40 diodes in series now that just about cuts off the amp when keyed, no signal.(idle) This is about 19 volts positive on the cathode = -19V on the grids ref to cathode.   I'm gonna add another 50 diodes and see what a total of 45 volts does for class C.

Talk wid ya tmw -

T

Tom ..OK on the difference between  quiescent and standby idle...It makes sense to me now...I await your results...

OK Steve -

I plan to get it on the air over the next few days for some shake down runs. We'll let ya know.

BTW, another benefit of the grounded grid configuration is the RF negative feedback generated by the cathode drive power - cleaner. This power is not wasted and even shows up in the output.

Also, I just realized that a GG amp running in this triode configuration for RF AM is no different than running them triode connected as modulators for AM audio. In triode connected modulator service they sound wonderful.... just like the triode connected 813's.

I'm cornvinced that a GG 4X1 with class C bias is a sleeper config for RF AM use.   Very simple circuit and supporting infrastructure.

T

Here's some shots of the bias diode board that goes in the filament transformer center tap. By shorting out diodes, it changes the tube's operation class from class AB to B to C.  The rotary switch gives about 11 bias positions.  The bias is rock solid at all currents since it is the drop across the diode junctions. (About 0.5v per diode drop)  I used fast recovery 3A 1KV diodes cuz that's what I had available.  Any diodes will do with at least 1A rating. The voltage rating can be as low as 50V per diode.

I measured the bias voltage when the amp is keyed and it is selectable form 0 to 23 volts.


At 3500 volts on the amplifier:  (this is my recommended voltage for AM operation by experimentation - 3,000 volts will do OK too)

At 0 volts the amplifier idles at 500 ma.  The next step is 250 ma and then 125 ma. This is good for ssb operation.


For AM, I found a bias of about 18.5 volts works well. This cuts the amplifier off at about 5ma of idle resting current. (no signal)
The higher biases are for CW operation in hard class C. It gets increasing more difficult to drive the amp above 18 volts of bias, so 18v is a good compromise for AM operation - if you have plenty of drive available.  

Steve: You will probably want to run slightly less bias with two tubes when using the FT-102 as a driver. Maybe 12 to 15 volts will do for you. The less bias, the easier to drive, but then the plate dissipation is higher.

Pics below of the diode board:

Latest pic:

Notice the HV meter mounted on the top. I wanted to make it REAL clear... :-)

It's so easy to work on with that side Plexiglas panel removed...

T

Tom,
You should find a way to monitor air pressure inside the chassis to get an idea where you stand when in QRO to make sure you don't trash a tube. Also would be good to know the air temp above the tube. A thermal couple on a small ua meter would be easy to calibrate. I have a spool of thermal couple wire around here somewhere. fc

that is bad brotha. That there gonna wipe out the moonwalk.  8)

Tom, I have buried somewhere some interesting articles on variations of typical  tetrode/triode amplifiers. You may be interested in:

"The Class 'C' Linear Amplifier" by D.O. Mann w6hly/w3mby
in CQ, March & April 1964

"The Cathode Driven Linear Amplifier" by Bill Orr w6sai and William Sayer wa6ban
in QST, June & July 1967

"The G2DAF Linear Amplifier" by C.W.O. Joseph Dempsey wa6jcm/4
in CQ, March 1966

Some  very interesting reading. Bill Orr discusses a simple way to control RF negative feedback, power gain, linearity etc. In "The Class 'C' Linear Amplifier" D.O. Mann talks of peak efficiency of 85%, 20 db gain, -30db IMD w/o negative feedback...

If these CQ articles aren't available (QST is online I think for American Radio Ripoff League members) I could scan and try to post them, or mail them to you on cd.

As Don KYV mentioned elsewhere, a reduced carrier/controlled carrier am rig driving something with huge PEP capability could be an interesting exercise. The Drake T4 was very effective on am driving a linear with a carrier of about 8 watts that would talk up to 50 Bird Watts.  Then run the amplifier essentially at ssb levels. Many corntester SSB rigs transmit more than that much power from uncontrolled blower noise!!! The Drakes were capable of decent frequency response without a lot of effort.



Hoooooooooooola!

Frank -

Yes, safety features are the next step. I like your idea about thermal alarm/shutdown. I have a sensor diode hanging over my other linear's final which turns on an alarm when it gets too hot.   The reason I installed it was cuz I once ran it w/o air - the blower hose pulled out. It got so hot that solder weeped out of the fil connnections.  I will do something for the 4X1 rig too.

Also need to build up that input overdrive snubber for the MS-150 SS amp.


Derb: "The Moonwalk" wud be a good name for a rig too... :-)   Right now I still have "Mr. Ugly,"  "Dr. Love" and "Fabio" running in the shack.


Fred:  Those sound like very interesting articles. Sounds like someone "discovered" class C AM linears way before I did... :-)  I remember reading that article by the British guy somewhere before.  Tell ya what... if you cud scan those articles on your printer/scanner and email them to me, that might be easier than CD/mailing. Let me know - thanks much.  (email OK on QRZ.com or profile here)  About the super-modulation: The controlled carrier thing sounds interesting cuz it wudn't overload a diode detector like a 200% balanced modulator would, but then the hedrodynes get funky. We'll have to experiment with the best way to use the headroom.


BTW, I found another used 4X1 (4PR-1000) from a guy that may work out and replace the soft one in the lineup. I'll know in a week. Actually I bought two used ones just in case.  Hope to have the new amp shaking on the air this weekend.


73,

T

OK Tom. Do you need the Qstreet Bill Orr article too?

Have you considered balancing the bias/idling current between the tubes? Granted the tubes are rugged, especially the 4pr1000's... did it with six 6lq6's once, it just seemed the thing to do.

Another advantage to your amp is the multipile tubes lower the plate Z. 4x1's get pretty hi @ 6kv but you're dividing it by 4. The high total plate capacitance would become a factor on the higher bands... but on 160 and 80 it's gotta be one impressive amp. How stiff is your ac supply? hehe

Hi Tom and others ... this has been an intresting thread, esp about op an am tx with 'leenyar' amp that is only partially linear ... you mentioned experimenting with a mix of controlled carrier to bal mod to high level plate mod rigs ... I have (to me) an new additional wrinkle .. I have come up with a way to vary the amount of controlled carrier from none to "some" in a plate modulated tx .. some tbd .. I am incorporating it in my current construction project ... I hope to have it ready to test soon ...73 ...John

Hi Fred,

Yes, the Bill Orr article about ways to control negative feedback sounds like something I may want to do -  If it's not too much trouble... TNX.

On balancing the tubes - I wud have done that but I'm using ONE fil transformer to feed all four tubes. The bias goes in the fil CT, thus no individual biasing. I don't want to lift the nice thick ground straps to the screen/grids and play with external supplies either.  BUT, three of the 4X1's show nearly the same plate color during idle and full power, so hopefully the forth tube I get to replace the soft one will match and balance with the others reasonably.

I found with 6KV it was too "animal" for me.  3,500v under load gives a beautiful dull orange plate when running full carrier with moderate air. I think I have the plate impedance matched right too at that voltage cuz of the good efficiency. I think I found the sweet spot of the lashup, including the MRF-150 driver amp.

John:  I'd be curious how you will be swinging the controlled carrier. Is it a grid driven amplifier with control of the screen and/or grid voltage you're accomplishing this with?  Might be a little harder with straight GG unless it is done in the low level stage, like at the FT-102 driver. Now that wud be fun to experiment with I think.

The only thing with controlled carrier is the annoying up and down sound of hedrodynes when using it.... :-)  Everything is a compromise or I guess we'd all be using the same thang eventually.

T

Tom,
I had a few emails with Rick Measures on NFB in GG amps and he told me there was problems with the Orr method.
At 6 KV the tank circuit would need more L running at higher z.

I hear you in there using Quadzilla on 3885.  Nice signal

Heard you, Steve-HUZ, and Don at 20 over here around nine thirty. Steve-QIX was 40 over,. Quadzilla sounds really good.
Shelby KB3OUK

John and Shelby:

Thanks much for the nice reports, OM!  These were the first contacts made with the new amp.
I was beaming west with the high Yagi all night, so glad you were hearing me well locally.

The new amp ran flawlessly all night. Real pleased.  The only problem so far is one of the vacuum variable shafts froze up and needed a new shaft. (Don't be talking 'bout Shaft)  I found that at 3500V, Quadzilla is about equivalent to my 4X1 X 833A plate modulated rig, (Fabio)  but easier to use...and it's prettier to look at... :-) 


Big group in there tonight on 3885 and still going on. Maybe 20-25 stations including Calif and Wash state.   Just love to hear that AM DX come in.


Frank:
Yes, I did add more tank inductance when I tried it at 6KV+ to compensate for the higher impedance requirement.  Still, the plate dissipation was too high on AM and I didn't like being on the hairy edge of destruction... :-)   3500V under load is a nice, controllable level with dull orange plates for OB xmissions. I increased the air flow with the Variac and see very little blower noise on the scope when using it on the air, so all set. Quadzilla is basically finished for now. The next challenge is making an effective input power limit snubber for the MosFets. I will be trying your design.

Later -

T

Tom,
I was listening between 10:00 and 10:30. Conditions were great. Now you know why I like running afterburner mode. The 4CX3000A is almose 4, 4-1000As. at 4000V I can do the same thing. KISS. now that i have a bit more floor space showing it might be time to put the linear on the bench and do a little work on it when I not playing with the 4 other projects I have going on.   

Sweet Jebus, that first pic of the closeup with fils lit is beautiful. Hope you don't mind if I shag it for a wallpaper on the pc.

Regarding the post where you melted the slobber out of the pins on another amp, or TX, whichever, how about a pressure sw setup to babysit the blower. I never had any faith in sail switches, thermal devices in the outlet air are way to slow to prevent nuking the tube base, but a pressure sw cutting the control voltage will kill the juice if the blower starts to slow down, or air pressure gets lost in any way. On my old 2x4-400 leenyar, I had a pressure switch series wired into the coil holding voltage for the mains contactor. It was setup with a bleed off tee to keep it accurate and it knocks out the entire unit if the box pressure drops below 12"WC.

Just a thought.

If your interested in going past just the thought, all I would need to know is what the minimum box pressure needs to be for your super rig, measured with a manometer, and I could look up the right p-switch to do the job.

73

heheheh - Glad you like that pic, Frank!  It's my favorite of the whole batch too. I reposted it below.  It would make a good screen saver for sure.

OK on the air sensor switch. That may be a good way to go.  I'll give it all some thought.


John:  Yes, for controlled carrier operation, 3db would be a transparent amount of carrier swing and also take a huge load off the steady state carrier by using 1/2 power. I like it. Think I'll talk with the HUZman and Bill/DUQ  about modifying the NE-602 circuit so that it can be goosed with a DC offset controlled by the audio. I suppose a certain audio threshold cud trigger a 3db carrier increase. It sounds simple enuff in theory to me....   This wud help boost integrated carrier efficiency and tube color reduction, markedly.


Frank:  Yep, your GG 4CX-3000 is probably the simpest way to duplicate the 4X1 amp. For viewing, you cud always mount a single 833A and use a few miirors looking at each other to make it look like a dozen.    I tried a large, long mirror behind the 4X1's the other day and it was stunning. You cud not tell the difference - there were eight in there... :-)

T

Sounded great last night Tom. That inline four is the way to go. It works well and looks good doing it. You were at least 10dB louder than anyone else and the audio sounded great. Good conditions too. The west coast guys were rolling in here at 10-20 over 9.

I checked out at about 1:30 AM and there were several still in there.

Tom was pretty good, but Don KYV gets my vote for the strappinest signal into NJ last night.

Three dB or so shouldn't be noticeable, given the right time constant(s). Some have done this in past decades with rigs like the DX-60, etc. I recall one guy who had his set up so he could vary from full carrier control to none (pure screen modulation).

yes I agree with 3 db as an easy figure of merit ... time constants I am trying are .5 msec attack and 100 msec release ... what I am trying is similar to what you are discussing with the NE602 circuit but with a 6S4 in the screen circuit of 2 - 6146 .... first attempts will be dc shifts and then if that works well may also try a bit of audio as well ...we shall see ...73 ...John

p.s. I AM NOT trying to steal your thread ... just kicked off this idea   ... by the way Steve, the stock DX 60's seen to generate about 9 or so db of controlled carrier and at times is annoying and other times is impressive ... a most curious hobby, this   ... beefus

Tom
I would think you could rectify the positive peak and feed the voltage into the dc carrier voltage as an offset. The trick would to be selecting an attack and decay time that didn't introduce distortion. Email me your circuit.
Tom, you missed out on two 4-1000As at the flea. $75 each

Frank,

Here's the NE-602 circuit.  It appears that pin 2 wud be the place to inject the controlled carrier signal.  I agree that using the positive peak rectified is a good idea. We wud want a "linear" ramp up as the voice signal increased. 

http://www.amwindow.org/tech/htm/602mod.htm

A sample of the audio from pin 1 then rectified thru an R/C time constant is what's needed.  Not sure if we wud need another IC or transistor for isolation and gain.

Let me know and I'll modify my NE-602 in the FT-102 and test it at 20W before trying it with Quadzilla... :-)


John: No problem with "hijacking" the thread. I think the opposite way...I've always considered it a compliment whenever someone comments within one of my threads, no matter what the subject. It's that way in the real world and subjects are always changing, so why not?  :-)  Keep the new ideas flowing, no matter what they are.


Good luck with the tube version of the CC idea.  For linear (or low efficiency) operation it really is a great idea - if it can be set up transparently. Even for plate modulation, I'll bet it cud be useful as well.

I'd like to play with this circuit and see how far we can push it before introducing meaningful distortion. I figure one pot for the db carrier level insertion and another two more pots to play with attack and decay time constants - at least until it can be dialed in.

BTW, Frank, OK on the $75 4X1's.  I already have two on the way for $90 each, so I'm all 4X1ed out... :-)   Any other gud stuff there? How was the crowd?


T

 

Plenty of AMers but not a lot of stuff worth looking at. Lunch well attended but food was poor. Too much salt and service sucked. I must have done a quart of water when I got home. It was fun though.
let me study that schematic a while. I'll get back later.
Warren picked me up a slab of copper so I can mount erb2 holer and do more testing with the HPSDR set up.

a good idea with the NE602 ... my experience with signal processing (vox circuits especially) would have me wanting a full wave rectifier for the offset voltage  .... tends to remove 'gappiness' from the response ... don' t know if you have balanced or unbalanced audio available ... could be a good time to incorporate balanced ...just some thots ...by the way, thanks for the joining in from all... very rare these days ...73 ...John

Tom,
The carrier inject pot. Which way do you go to increase the carrier output.
Does higher resistance increase the output? Q 1 is not biased properly. It is set up like a switch not a linear audio amp. I bet it is temperature sensitive  the way it is.  I would add a 220 ohm resistor in series with the emitter and change the 100 K Base resistor to 10 K. This will make it biased in the center of the voltage swing and give it temperature compensation with a gain of 10. If that is too much gain increase the 220 resistor. Need more gain decrease it.

Frank,

I measured the carrier inject pot. As the wiper of the 1 meg pot is moved away from ground, the carrier power output of the FT-102 goes up. 
So, higher R at pin 2 = higher carrier power output.

OK on Q1. I didn't use Q1 in my rigs. I didn't need it cuz I've got 1 v audio and it's enuff to drive the NE-602.  I think Bill added that afterwards.


I just checked the FT-102 / NE-602 freq response and found it's flat from about 1 cycle (as low as my sig gen goes)  up to 60kc.  It looks like a perfect waveform with the little "wavelets" when the modulation goes over 100% negative.  The modulation percentage is virtually unlimited, depending on where the carrier level is set.   ie, 20 watts carrier w/ 150 w peak  or 5 watts carrier at 150w peak, etc.

I will be using the 1 volt audio level from the input jack of the board for the rectified audio feed. You can take it from there.

Tnx.

T

There's no problem with Q1. Many, including myself, have been using it for years with no problems. I measured response out past 500 kHz with the the 602 circuit. When installed in the 102, the response was still good out to 100 kHz or so.

Steve,
Not the way I learned to bias a transistor to work over a wide temperature range. Gain is usually Rc/Re . Imagine the resting collector voltage over temperature. What is the gain of the stage as it is over say 25 degrees.
Tom ok on the 1 volt of audio. Let me give sleep on it.  I think you will need a diode or two a transistor and a cap.

I like the turns counter on your roller inductor!!  How graphic can you get?

Al

OK Frank -

Should we add in an RC attack and decay circuit with pots at this point to find the best time contants or just get it going first?  John suggested time constants of 0.5 msec attack and 100 msec release ... Maybe we shud start with those numbers.

I'll build it on an outboard PCB so we can experiment. 

I actually measured 3 volts p-p of audio available.


* I built up your power snubber tonight. I'll try it out tmw. For diodes I used those same big ones from the MOSFET solid state PDM rig project,  STAA3006P  / CO349.  Steve/QIX said they were quite fast.   I used two small 18V transorbs in series to make 36V. They will probably blow out, but at least I can test it at QRP -  I'll order some bigger ones if it works OK.    Built +- 25V supply for bias.


Al:  That's a  Guestimate brand turns counter.... :-)    Actually, the red marker dots get me exactly to the match on each band quickly.  But I do have another counter - I shud add it in now that it's bell and whistle time.
T

Tom,
Check the junction C of those diodes they may act like caps and run warm and suck your drive down. I sent you a marked up schematic. There is an error though. The emitter resistor is too large try 1K. You can easily outboard it. I hope it doesn't load your audio too much. Monitor the transistor base voltage to see the time constants. fc

LOL. No need to imagine. The circuit has been in use by many for about 10 years. If there was a problem with it, I'm sure it would have showed up by now.

Do what you like but a beta limited switch has a small linear range and unstable over temperature..

Copycat  :D

(http://images.tigerdirect.com/email/wem1865/wem1865mastdd_01.jpg)

Derb named it.

It was from his subconcious, NOT a copy, don'cha know.  ;D

Someone from Tiger Direct has been reading this forum or listening in on 75 meters.  ;)

My people have already contacted their people concerning a Quadzilla infringement.  We'll probably settle for $1 billion (slush fund) and celebrate by taking everyone on the AM BB to Maui for a much-needed, month long vacation.   ;)

T

be sure to invite Sir Francois De Slabsinister of Nottingham first!

Frank,

BTW, for the RF snubber/ power limiter to drive the 600w MosFet amp, I ended up using a simple resistive pad to go from 100w down to about 15w pep.  I added a small switch to adjust it slightly for various rigs.  Used a 60 ohm glow bar and some carbon resistors.  Got a pretty close 1:1 for the exciter.

So now the FT-1000D at 200w and the FT-102 at 125W won't blow out the MRF-150's no matter what. 

I think someone here suggested the straight pad - don't remember who, but it was a good idea.... fool proof.

T

I won't believe any of it until I see the Plexi-King trademark up in lights!  ;D