Simple Valve MW "Signal generator"

[boiss]

The variable bit is to get the screen grid volts right so that the modulation works well. I found that the 1M /82K worked just right with my PL36 but this would vary with a different valve. This bit is a definite suck it and see, the valve I used had seen many years use and the brown base was very charred but it worked OK. I tried the same with a couple of 813s one was OK with a low level of achieved modulation but the other one needed a much bigger voltage swing which is why I used another valve to amplify the audio.
Mike