Pitch Oscillator not working

Posted: 4/10/2018 1:04:53 PM

Joined: 4/10/2018

I have been trying to make the theremin schematic given by Robert Moog as a part of a course project. Today I wanted to test the pitch oscillators on breadboard. However the BJT available to me is 2n2369 and I used those, for the variable inductor I used 100microH inductor and the capacitor was modeled at 10pF. Although according to the simulations I performed on spice(for the BJT 2n3904) the circuit should work however on performing the experiment I saw no oscillations. In fact the emitter voltage was around 11.6V instead of -0.6.Can anyone please help me out with what the problem is??
note: The inductors used are the standard colour coded inductors, not sure of what they are called.

Posted: 4/10/2018 7:20:51 PM

From: Colmar, France

Joined: 12/31/2007

Most probably a wiring error, i.e. switched base and collector. What are the base voltages at both transistors? Both should be around 0V. In case one base is around 12V instead, check the RC feedback network for errors. And make sure that the common emitter resistor is correctly wired towards -12V.

The 2N2369 is not suited for that circuit. It’s maximum Vce is 15V, but when everything oscillates correctly, Vce might exceed 24V. You might have roasted them. The 2N3904 is available at each street corner. Go and buy these.

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