New 4-1000A modulated by 4-1000As AM Project - Fabio II Reborn

[K1JJ]

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  

[KA0HCP]

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

Viva Fabio II!

[W4AAB]

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!!

[steve_qix]

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

[K1JJ]

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

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

[w1vtp]

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

GL, Al

[KA2DZT]

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

[KL7OF]

Izzat an easter egg in the grass?

[K1JJ]

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

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...

T

[ka4koe]

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



FEEELEEP

[Opcom]

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

Viva Fabio II!

Thanks a lot. I had forgotten it.

Too bad about the blowup after all that engineering.

[K1JJ]

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



FEEELEEP

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

[K1JJ]

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:

[K1JJ]

MODULATOR DECK  pics 1 & 2:


RF Deck Pic 3:

[flintstone mop]

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

[W3GMS]

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

[KM1H]

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

[K1JJ]

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

[KM1H]

Well Tom, I wasnt considering "conservative" operation

You coming to Nearfest?

[steve_qix]

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.

[K1JJ]

Well Tom, I wasnt considering "conservative" operation
You coming to Nearfest?

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

[K1JJ]

More general shots:

[steve_qix]

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.

[W3RSW]

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.   

[K1JJ]

.... 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.

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