The above circuit, whilst it works, is GREATLY INFERIOR to Lev`s Oscillator for Theremin use. The above simulation waveforms - Red Sine = voltage on L1:A, Black Sine = Voltage on Q1:D, Blue square wave is current through L1:B and Q1 (10mA, 5mA average) It should be noted that this current is through the `tickler` winding which has low R and L (100mR and 39uH max)
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so thermal and other problems should be minimal. Not physically built or tested in this form, but FET model is a good manufacturer supplied one which I have found reliable. Best to look at this schematic together with data on the RCA. Waveforms from first filters - Note, differential outputs have been genersted, but this is not strictly needed - one could take the lower [R4(2)] signal and use this directly: And finally - differentially combining the signals, and sharpening the filtering at the opamp, one gets clean audio (the above is shown with 170kHz and 172kHz input signals, giving 2kHz audio out: One can also add the 4-6 winding to any others giving additional range (for example, add 4-6 in series with 2-3 to extend somewhere around 50uH to this range available. great work!. but it appears the your tickler has a much lower inductance- whereas in RCA they are about the same. 170-180(ish) mH. and the RCA osc coils windings are in two layers with one on top of the other. The diagram for the 421F106 leads me to conclude that is is a single wind with multiple tap points. Fred, Im no engineer (should be my signature!) but couldnt these differences have an effect, albeit a subtle one, on the tone I dont think that I saved it, (and I may be wrong) but I recall another, or possibly followup email where Uncle Howie recommended against changing the coils at all. 76 turns of #26 magnet wire on a 1. 5" form X 2 layers (with about....
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