4-1000A grid driven transmitter layout

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KM1H:
What mode is this for and what is the driver?
As a linear or Class C you can run swamped grid input and do away with neutralization which may be a problem on 40M. Its a touchy tube to layout for stability in conventional grid driven. I built many swamped grid 4X1's in the 70-80's, one and two hole and 160-10 for most.

In GG it becomes a serious drive hog, requires a tuned input for any decent efficiency and IMD even as an AM linear, especially at such a low voltage :o

Carl

K3YA:
I have both a GG and a plate modulated grid driven 4-1000 on the air.  The grid driven final was also built to be also run as a swamped grid AB2 linear but that proved to be a troublesome and dirty mode of operation and was abandon long ago.  I talked with several other folks running 4X1 in grid driven linear service, including Tim HLR who ran his big rig in that way sometime, and it wasn't as simple as it looked to make it work well.  Here are a couple other thoughts based on my experience.

GG is a LOT easier to build.  However 3500 plate voltage is a little on the low side.  At that voltage it will be need a lot of drive.  A Ranger would probably drive it OK and you may "get away with" no tuned input if the connecting cable was short.  A solid state rice-box would need a tuned input and would be straining.  I have 5.5KV on mine and at that voltage it's quite easy to drive.  For easy, Grounded Grid would be my first choice.

Class C plate modulated would do a much better job overcoming summer static. With a modulator, screen and bias supplies it's several time as much work to build.  3.5 KV is still not very high for that tube and I wouldn't expect much trouble with neutralization or otherwise taming it.  I use the "bridge neutralization" circuit from the ARRL and west coast handbooks and it requires no retuning going from 160-20M or even changing tubes.  With 40M as your upper limit lead length and layout is not that critical.  For QRO this would be my choice.

Parts layout is determined by the size of the components on hand.  I do like to mount the tube at the front of the chassis and provide a window in order to monitor the plate color and show off that cool looking bulb. Also think about keeping heat sensitive parts away from the tube or protect them with a heat shield.

The Slab Bacon:
Down on the lower bands the 4X1 is a pretty docile tube. My big rig is grid driven with no neutralization and is completely stable. But..............
It is only built to run 160, 80, and occasionally 40m. It sees 90% of it's duty on 75/80m phone and runs along happily on 3400v.

DMOD:
Here is a companion thread in which Clark is building a linear Amp with a tube I sent him in Trade:

http://amfone.net/Amforum/index.php?topic=31647.0

Phil - AC0OB

N4LTA:
This will not be a linear amplifier. It will be run Class C and either plate or screen modulated.

It should loaf along at 400 watts carrier. I was planning to build it grid driven. I will also build a driver and would think 60-70 watts would be plenty either GG or swamped grid driven.

It will be mainly run on 75 meter am.

What do you think?

Pat
N4LTA

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