B3 dosen't seem to work

Hello everyone, I would like your kind attention to help me solve a problem.

I live in Italy and recently I bought a second hand B3 theremin as a present for my brother, they've sent it to me from an other city. The guy that sold it to me seemed honest and he told me he used it very little and that he would have gave me also the right power supply for it. But now that I have it here I tried it with a guitar amp and a jack and it wouldn't sound at all. I tested the adaptor with a computer charger and it was working, the specs of the adaptor are: IMPUT 220 V, OUTPUT 110V, Power 8VA, MAX ta 45°C.

At this point out of desperation I think I've done something quite stupid and I tried a plug adaptor with no voltage transformation, and it was finally giving sound, but then I heard a pop from the socket and I unplugged it immediately. Do you think I burnt something in the plug and that I should change it know?

I also tried with a universal adaptor I bought from a chinese shop and still it wouldn't work. Do you think it's possible something broke during the transportation? Is there anything I can do to get it working?

Thank you in advance for any help.

Eterno riposo, concedere a loro, o Signore, e lasciare che perpetua risplenda ad essi la luce
 Maggio le anime dei fedeli defunti attraverso il ricordo di Dio, riposa in pace, AMEN

Hahaha, that's a good one, anyway I just opened it up and changed the power supply with one with an output of 12 V and 300mA and now it kind of works but for some strange reason it does the opposite of what it supposed to do, so it would sound just when I touch the volume loop and make the low notes as I get closer to the antenna, any Idea of what's going on?

You most probably modified the internal wiring slightly which is enough to trouble the very sensitive volume RF circuit. But there is an internal potentiometer on the volume section which should allow you to compensate and to fix that. The potentiometer is very sensitive, too, thus you should mark the initial position before trying to improve thinks millimeter for millimeter.

Very helpful thank you, I'll try and see what happens. It's strange because I didn't touch other wires beyond the one from the power supply.

Thierry is it the small light blue plastic disk I have to turn?

In my b3 it is white, but color doesn't matter... Before you open a theremin to fix or to adjust it, you normally should have enough knowledge and understanding in electronics to identify circuit components and to know what their function is in the circuit. If you aren't sure, take a picture of your open B3 an I'll show you.

Holy Moses!  While there is nothing inherently wrong with the "dead bug" approach to prototyping, I'm shocked to see this laborious technique employed on a production model.  Dan Burns, or the people he employs, must have all the time in the world.

“Eterno riposo, concedere a loro, o Signore”

I always asked why use static prone FET’s and often the answer was they act like a vacuum tube, I scratch my head. Likewise why use this wiring approach and the answer must be it is like the wiring of the original RCA theremin, again I scratch my head. All these years and this is the first time I have seen a photo of this creative approach. It plays and sounds good as so many have attested.

I need to update my 13 Theremin Myths list.

Christopher

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