i just finished building the Em Theremin with the Article by Robert Moog. I used some golden Coils from "Kaschke" here. For the Pitch and Volume Antenna i use the Bourns 6300 Series.
When i turn it on i here nothing. As suggested in the article i used a multimeter with the following results:
Outputs of U1 and U2: +- 12 V
Collector of Q1 to Q8: 12V DC, Emitters of Q1 to Q4 and Q7: about 0,6 V DC, Emitters of Q5 and Q8: -2,5 VDC
AC Voltage across L5, L6 and L11: <1 VAC (should be 10 or so)
DC Voltage at R24: -0,2 V (should be around -0,5V)
I checked the VCA with Pin 12 of U3 to ground: I hear a very weak oscillating signal which can be tuned by the Pitch Tuner Poti and the slug of L6. And, (and seems strange to me) it can also be tuned by turning the slug of L11 but nothing happens when i turn L5 (which should be changing something, because its the VPO, right?) When i connect pin 12 to -12V the signal should dissapear. But its still there...
And, when Pin 1 is normally connected, the Pitch and Volume antenna do not work and i can here nothing but wind.
I double and triple checked the circuit but i cannot find anything. And i have no oscilloscope, but i hope i can fix it wothout one.
Any suggestions how i can find out in which part (VPO, FPO, VCA etc...) the problem is?