On Thu, 30 Aug 2007, Jack Schmidling wrote:

Is it convenience or the laws of physics that modulators are always two tubes
in push pull?

I have an extra 811 and socket and was wondering if there is a way to use
this to plate modulate my 811 cw transmitter.

The most practical approach (someone else mentioned this) would be Heising
modulation. The modulator 811 would be, like, in parallel with the RF amp
811 and both fed with DC through a fairly big choke (10 Henry or more).
There has to be a dropping resistor that eats up some of the DC voltage
going to the 811 RF amp, and you'll need many watts (5+?) of audio to
drive the grid of the 811 modulator.

Modulation transformers are still made by Peter Dahl (?) in Elpasso,
Texas, and will be several hundred bucks at least. I think I have never
seen a single ended modulator circuit unless it was for very low power.

pics of 811 project at http://schmidling.com/radio.htm


js


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