4-1000A grid driven transmitter layout

[N4LTA]

Older editions of the ARRL Handbook describe running a GG amp in class C. In fact thats is how they describe a GG amp - Run in class C and AM modulated. GG does not mean the amp is linear - it depends how it is biased.

The older Handbooks indicate that GG is only worthwhile if you have excessive drive to pay for the simpler circuit (they are talking about AM operation.

If you plate modulate a GG amp that is biased for linear operation, you will get non-linear modulation.


Pat

[kb3ouk]

As I saw on here a while back, back under the kw input rules, it was possible to run a carrier power that was over what you normally got from a kw input if you ran a grounded grid final. The tube that was mentioned as being used was the 304TL, which also needed to be biased to run well in GG service. But how it worked was the drive that was passed through the final added to the power that the final tube produced. The final would be working at a kw input, but the drive power would add up to that carrier to give more power.

[KM1H]

A 100W driver is more than enough to drive a swamped grid Class C 4X1, about 500-600 Ohms will do it depending upon plate voltage. A 4D32 or a couple of 6146B, both at 700V, should have plenty of reserve. Design the pi net to directly match it and dont worry about no stinkin baluns

Carl

[The Slab Bacon]

Pat,
      If you really want to get down with yo bad self, build a GG 2-holer. I have a filament transformer here for that specific application. If you're interested, you can have it for the shipping. I'll fire it off and test it, give it a hi-pot, box it up and send it off your way.

You will be da boss wit da hotttttt sauce ! ! ! ! ! ! ! !      

[KM1H]

Better to use it on a 3CX3000A7 or F7 if you dont need to watch the light show

[KC2ZFA]

Grid driven, but NOT swamped. Just biased way down in class C. (-150 or 200v IIRC)
The heavy biass and low resting carrier screen voltage is what keeps it so stable. there isn't even ANY control grid circuitry in the final deck. The grid lead comes right off of the socket into a piece of RG-142 double shield coass and goes out up to the exciter where the drive and biass is sent down the line to it.

Slab, how long is that RG-142 run ?

Peter

[The Slab Bacon]

Slab,
       how long is that RG-142 run ?
Peter

Peter,
          If memory serves me correctly, without opening up the transmitter decks, I would say it's somewhere between 12 and 18". Also I peeled some of the clear outer skin off and soldered ground lugs (and grounded them) just about everywhere I could.
So that way the floating length of the coass is no more than a few inches for it's entire run. Kinda like running through a piece of RF resistant pipe for sake of analogy.
This way there is also no chance of the outer braid "going hot" at some wierd frequency and the final then passing it.

[WA1GFZ]

What no magic beads on the coax?

[KC2ZFA]

Thanks Frank.

And the capacitance of the cable is in parallel to the tube's input capacitance, right ?

[The Slab Bacon]

What no magic beads on the coax?

Thanks Frank.
And the capacitance of the cable is in parallel to the tube's input capacitance, right ?

C'mon, Frank, with the outer shield slobbered to ground every 2" or so, it shold have no trouble staying at RF ground potential and maintain it's shield effect.
(not to mention stay EXACTLY where you want it ) Don't forget that the inner conductor is carrying both RF and DC by design. That double shield silver teflon stuff is just great to work with. The silver plated braid just sucks the slobber right in, and with the teflon insulation, you can really pour on the heat without having to worry about melting and shorting it! ! !

Peter,
        the small amount of capacitance from the coass is not even noticed at those lower frequencies. The tune cap in the driver tank is more than capable of tuning it out.

[N4LTA]

Slab,

What type of driver tank are you using - a simple parallel tuned network with the cold end grounded through a capacitor?

Pat

[kb3ouk]

http://amfone.net/Amforum/index.php?topic=16319.0

Here's a post on Frank's 4-1000 rig, includes a schematic of the final amp.

[WA1GFZ]

just being a jerk Frank

[The Slab Bacon]

Slab,

What type of driver tank are you using - a simple parallel tuned network with the cold end grounded through a capacitor?

Pat

See attached PDF

[WA1GFZ]

I hope Frank lives long enough to wear out all the 4-1000s he got from me.
I hope I do also
I hope we all do

[The Slab Bacon]

I hope Frank lives long enough to wear out all the 4-1000s he got from me.
I hope I do also
I hope we all do

I do too! ! ! ! ! ! !

they are some tough bottles!!
After 12 years of running with the plate glowing pretty red,
I am still using the first one I bought when I built that thing!
I still say they are the best bang for the buck when it comes
to BIG power tubes. Good used pulls are still fairly cheap and
plentiful.

[WA1GFZ]

So you have not used any of the tubes you got from me yet.

[N4LTA]

If anyone has a 4-1000A that they don't need - I could use a spare for this transmitter.

I have one pretty decent looking pull that has no color on the glass.

Pat
N4LTA

[The Slab Bacon]

I have one pretty decent looking pull that has no color on the glass.

Light the filament off first and make sure it hasn't lost it's vacuuuuuuuuuum.
They do have a slight tendancy to develop leaks around the pin seals.

So you have not used any of the tubes you got from me yet.

Nah, the original one just won't die! ! !  It has outlived 3 plate transformers, though.