Re: Professor Theremin advert.
It looks as though the UX-120 is being used as a variable resistance in the anode feed to the heterodyne (IF) amplifier, progressively starving it of HT with movement of the "volume" hand. It reminds me of the line output transformer-fed filaments of thermionic EHT rectifiers! With their syndrome of no EHT if the LOP stage goes weedy for whatever reason. That would seem to be a topology available to Theremin at the time, so maybe that is what he did, adapted to US valves of the late '20s by RCA. Unfortunately, something rings a bell that the toobs listed are very much on the gold-star hit list of the fanatics.
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