How Theremin Components Work

How Theremin Components Work
On behalf of ExpertVillage.com my name is Mark, and we’re going to talk about Theremin components. The chassis that we see here are out of the Theremin to my right, this particular set of chassis didn’t have all of the tubes in it, I had robbed them for another project that I was working on, and this is one of my backup sets. The five tubes on this chassis, which is the oscillator chassis, generate the sound itself. The three missing tubes are 6J5s for the technical minded those are triodes, they haven’t made that tube for many-many years and there’s still plenty of surplus from World War II and the 50s that’s available. These two 6J5s are the oscillators and they run at approximately 180 to 200 thousand cycles per second. And for reference that would be about half the frequency of the lowest setting on your AM band or not too far from where submarines use to transmit. These two tubes generate frequencies that are mixed together in the 6SN7 which is a dual triode; it’s sort of like two 6J5s in one package. That sound is then detected by one-half of the 6H6 dual dial tube, the other half of the dual dial is used to detect a voltage for the 6J5 oscillator for the volume circuit and this operates at about 430 kilohertz. Now the reason for the difference between the volume and the pitch frequencies is you don’t want them mixing with each other, you want them to be separate enough, you don’t want one to be half the other or twice the other, you want them to have no mathematical relationship if possible. Underneath the chassis we have circuitry not unlike what you might find in 1930s radio set, if you look underneath. In this particular unit the bright orange components are the capacitors, the striped parts are the resistors. This is a tuning capacitor in the front that’s for fine tuning the frequency when you tune the instrument. This is a pilot light on the side which shines through a red jewel like you would find on an old fender guitar amplifier. I’d even used shielded wiring, this came out of an old church organ and the rest of the components, not many of them but that’s what generates the frequency for the Theremin. Now after we have this signal out of the volume control circuit, it comes to the amplifier in the form of this cable which plugs in to the chassis receptacle right here.