An Adventure in Oscillator Theory

[old_tv_nut]

My guess is that this is actually a transformer-coupled oscillator. The sliding short changes the inductance of the transformer, which is connected to invert the plate signal, thus producing positive feedback when connected to the grid. I think maybe the ground at the end of the transformer is theoretically not required, but serves to equalize stray capacitances on the input and output sides that don't show explicitly in a schematic. How's that for a guess?

http://en.wikipedia.org/wiki/Meissner_oscillator

[VintagePC]

Originally Posted by old_tv_nut

My guess is that this is actually a transformer-coupled oscillator. The sliding short changes the inductance of the transformer, which is connected to invert the plate signal, thus producing positive feedback when connected to the grid. I think maybe the ground at the end of the transformer is theoretically not required, but serves to equalize stray capacitances on the input and output sides that don't show explicitly in a schematic. How's that for a guess?

http://en.wikipedia.org/wiki/Meissner_oscillator

I think you might be on to something there... Definitely explains the use of that tickler gimmick on the grid plate... I can't imagine that being the capacitance part of the tank circuit as it would be incredibly sensitive... one wrong bump and the service guy owes you a new one.

That said, the ground in this system isn't actually connected to anything; it's just chassis which bears no connection to either side of the AC line.