Power Hungry

[W9ZSL]

Dang!  I'm still trying to recover from scoring major iron; a UTC S-22.  OK; 200 Watts audio. Done. I'm going to use my Kenyon 500 balanced to class B grids transformer.  So I go with 811As with 1250 volts on the plates. Drive it from my studio limiter.  Plot thickens with a package of chickens.

OK.  PA.  Got 2KV @ 300 ma max.  I have filament iron for an 813.  Need a tube and socket.

Even though the traditional 813 / 811A combos are happy at around 120 watts audio, the classic Collins modulation transformer was the cats if the voltages matched to the optimum impedance ratio.

Here's my question.  Can I realistically run a single 813 to at least 350 watts input AM with 811As pushed to 200 watts audio given the voltages listed considering the RF and AF have separate supplies with an S-22?  Give me room to breathe!  Remember each supply is 300 ma.  Too much fun.

[kb3ouk]

Datasheet for an 813 says 2kv at 200 mA give 300 watts output, or 400 watts input, so maybe back off the voltage a little bit, to say something around 1800 volts. 811A sheet says 340 watts out at 1500 volts with 4.5 volts bias. That will draw 313 mA, but with the power you want from them, you have room to back off the current some.

[KA2DZT]

You can use a 4.2 volt zener in the filament CT to ground for bias.  I would run the 813 at around 1800 volts.  The S-22 is a good xfmr but I wouldn't push it much beyond this level.  You need a little head room.

Fred

[W7TFO]

Whenever you homebrew, keep in mind the 'Special' or S series transformers were the cheapest thing UTC built.

There was a reason the Commercial (CG) and the Linear Standard (LS) product were priced substantially higher.

73DG

[W9ZSL]

I'll probably end up with just over 1800 on the PA and around 1250 on the modulator.

[Opcom]

Whenever you homebrew, keep in mind the 'Special' or S series transformers were the cheapest thing UTC built.

There was a reason the Commercial (CG) and the Linear Standard (LS) product were priced substantially higher.

73DG

There's also the PA range, I believe the older invocation of CG, right?
Lots of that good "S" iron around here. never blown one up but don't abuse them either. All that old iron is getting.. old. All of it ought be used wisely.

[W9ZSL]

OK.  The S-22 is the definite ice breaker.  I could only do 125 watts with the VM-3 which I'm selling.  

Loafing works just fine.  I'm aiming at a solid 275 watts into the antenna at high-power or perhaps slightly higher.  With a single-switch to lower power, I'll be a happy camper. The switch was salvaged from a BC-1T I yacked on at the local station.  I was on the air when the beastie died.

Figure 1850 / 1500 on the 813 plate and 1500 / 1250 on a push-pull pair of 811As into the S-22.  My two Thordarsons and the chokes are all matched.  I can mix and match voltages as needed. 300 MA for both RF and AF.

Soon as the S-22 gets here, the build finally begins.

[W9ZSL]

The PA series was concurrent with the VM.

[W9ZSL]

Op, check out MY kitties!

[W9ZSL]

  I agree with everything and it's a "Can Do".  I'm not going to screw around with 20 Meters.  I have 3885, 7290 and 7295 crystals.  Going with the KISS "Bare Bones" as outlined elsewhere, VXO.  That makes the 813 input and the output Pi Net basic.

I have a classic 28 mh military rotary bugger but I'd rather build a PI around what I have on hand.  I can tune the output to the fone-bones and not have to crank. This is turning into a classic Junque Box Wonder.  I have some nice coil stock which will work. I know it will.  I bought it to use in this project to begin with years ago.  What goes round is finally coming round.  If a black hole sucks me in,   get over it.  Oh.  I can build some traps for my dipole with what's left over of the coil.  I'll have to get some pix.  I have a 300 pf @ 7500 for plate tune and over 2000 pf antenna load...conservative.  I believe the coil is at least 2" and #14 at about 8 TPI.  I have to double-check.  Here is where help comes in.

HELP!  Well, maybe not yet.  My strong suit is Audio so that S-22 is doomed.

[Opcom]

Op, check out MY kitties!

Pretty ladies are a joy!