How *not* to make a vacuum tube Theremin…

by Stephen Hobley on December 28, 2010

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I think that the humble coil has to be my favourite electronic component – You take some wire, and wind it round and round and make a radio, a metal detector, a tesla coil, and a theremin. And they look darned cool too.

For a long time I’d been thinking about trying to build something with vacuum tubes – as these have an inherent coolness factor too. So when I discovered the plans for a Vacuum Tube Theremin, designed by Mark Keppinger, I was hooked.

OK, so after getting into a little bit of a mess building the amplifier and power supply chassis I decided that what I really needed was a PCB for the oscillator chassis. This, coupled with my selection of #16 gauge wire proved to be a big mistake. First off the wire is too thick, and the PCB design required too many cabling runs.

As you can see (and hear) in this video…

Despite my best intentions it rapidly became a horrible mess.

The 3 Hartley oscillators are functioning, but all the EM junk being created by the wires is making it impossible to get a decent tone out of it. This picture shows the primary pitch oscillator (running at about 180KHz) featuring ghastly/horrible ringing.

So…. I have to strip it all back and start over – this time with #20 and #18 wire – I’m reliably informed by Mr Keppinger that this should be fine for the current carrying requirements. I am going to use some small pieces of PCB, but keep all the wires as short as I can.

Hopefully this should fix the nasty squealing noises.

If you are interested, here are the schematics for the amplifier and oscillator chassis (scroll to the end)

I’ll document the rebuild here as a guide to others that might try to follow me down the rabbit hole of tube electronics.

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{ 3 comments… read them below or add one }

clicclic December 30, 2010 at 4:19 pm

Wow that’s so great SJ is helping you wire up these projects – at such a young age too!

Stephen Hobley December 30, 2010 at 4:24 pm

She wants to…

She *really* wants to…

Philip Neidlinger August 15, 2011 at 2:29 pm

Your waveforms look just like mine…identical in fact. I built mine using the stamped chassis. Hartley oscillators are known for being harmonic generators.

Good luck!

Philip Neidlinger

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