Theremin project debugging

[Mihkel]

Hey. So it's been a few years since I've posted on this forum, but now I'm back and of course I need help.

I'm trying to build a Theremin based on the project on this site: http://www.pisotones.com/Theremin/Theremini.htm

At first I followed the veroboard layout, but got no sound and couldn't figure out the problem. Then I followed the original theremin's layout (http://www.pisotones.com/Theremin/imgs/FMK/Circuito3.jpg) and well... same thing. All I can get is a slight buzzing sound when touching the antenna. While resoldering the connections I accidentally disconnected the 27p cap that is parallel to the 15p cap and 100uH choke on Q3 and got oscillation that was affected by touching the antenna and turning the tone pot. But it was no theremin sound. I used 3k9 resistors instead of 4k1 and according to this site: http://www.instructables.com/id/Easy-theremin/, the 1.07k resistor should be 1k7, I have 1k6.

Here are my transistor voltages:

Battery 9.39V
Q1 (BC546A)
C:8.9V
B:1.25V
E:0.77V

Q2 (BC557)
C:9.27V
B:8.66V
E:5.28V

Q3 (BC546A)
C: 8.92V
B: 1.16V
E: 0.69V

And some phots:
http://www.instructables.com/image/FDY48U6HSXO9KK2
http://www.instructables.com/image/FKZ68YLHSXO9KK4
http://www.instructables.com/image/F8BENAYHSXO9KK3

Anyone care to rack their brain?
Thanks

[charbot]

Well, it could be a number of things...
Theremins look deceptively simple.  You need to remember that you are dealing with RF which is essentially black magic in my book.  Many unseen forces are in play.
First, If you are trying to tune this circuit on the bench, un boxed  with wires exposed, tools nearby, etc - like one would do with any other type of project- it is going to be hopeless.  You need to put it in the box/enclosure where it is going to live, wire it all up neat and tidy- like as if it were all done,  put it on a mike stand, move it away from all other equipment, power sources, metal, tables, other people, then try to tune it.   

I recon that if everything else is connected correctly and nothing is fried-  it is probably the inductors.   Maybe try different 'styles' of chokes.   From my experience, the larger the better.  more wire(usually very thin)- less ferrite.    

If you have access to a freq counter (even on built in to a multimeter)  you can probe around each transistor to see if the circuit is oscillating.