Yet another box of mystery – any guesses what this does?

by Stephen Hobley on December 14, 2010

Post image for Yet another box of mystery – any guesses what this does?

As a follow-up to my last Box of Mystery

This is the latest “thing” I’ve been working on – it’s still quite a way off completion, but it does look rather cool – anyone like to guess what it is?

Gotta love ye-olde-worlde-Jules-Verne-style tech!

Click here for a closer look

OK (so as worked out by Todd below) it’s actually a vacuum tube Theremin, following the design by Mark Keppinger.


{ 16 comments… read them below or add one }

Todd Harrison December 14, 2010 at 7:41 pm

You’re building RF notch filters which will use in-line vacuum tubes for signal amplification.

Stephen Hobley December 14, 2010 at 7:59 pm

Todd –

It certainly involves RF signals, and yes quite a few of the vac tubes are for signal amplification, but it does have a very specific purpose…

…using heterodyning.

Todd Harrison December 14, 2010 at 8:23 pm

Ham band receiver.

Stephen Hobley December 14, 2010 at 8:45 pm

Getting colder…

It’s more of a motion sensor than anything else.

(I was reading your website BTW – good stuff!)

Todd Harrison December 15, 2010 at 12:21 pm

A friend of mine guessed Sonar or theremin style audio amp.

Stephen Hobley December 15, 2010 at 12:52 pm

It’s a vacuum tube Theremin.

I’d been thinking about recreating the original Lev Termen / Leon Theremin design, but it turns out that some of the more esoteric vacuum tubes are no longer available.

This is following the “modernised” design created by Mark Keppinger.

The two large coils are for pitch and volume (smaller of the two) and the 3 coils are for the reference oscillators.

Winding the #32 wire onto phenolic form turned out to be way harder than first anticipated – the forms have no “grip” and you need to use a very high tension on the wire.

Todd Harrison December 15, 2010 at 1:20 pm

Maybe you could have spayed your tubs with 3M adhesive spray before winding.

Stephen Hobley December 15, 2010 at 5:10 pm

Y’know that thought did occur to me…

But I didn’t know if it would turn into a nasty sticky mess by the time I was done.
I do have some rubberizing spray that dries but still provides a “grip” I might try using this the next time.

Davey T December 16, 2010 at 6:24 pm

Looks like a nice piece of work. I wound large inductors like these for a Tesla Coil project using a slow speed drill, with a reduction gear, at a slight angle. There are some good tips on the Tesla coil builders pages. Are the transformers multi tapped to supply the needs of the bottles? Finally, it would be interesting to here the ‘warmth’ of the sounds it makes compared to the ‘Digital’ version which you can buy commercially, regards and keep up the great work.

Stephen Hobley December 17, 2010 at 12:42 pm

Yes the main transformer is a Hammond and provides 550V 6.3V and 5V supplies – along with a 125V tap on the primary winding – currently not used.

The output transformer as many taps on both the primary and secondary windings.

There are some good schematics/pictures here:

Jack Honeycutt February 16, 2011 at 10:21 pm

I *really* want to build a Keppinger tube powered Theremin. Please keep us posted!

Very Cool!


Davey T March 28, 2011 at 6:25 pm

Steve, On the odd occassion when visiting this page I get an AVG active treats warning and the page is blocked. I will try to capture the err mssge and let you know. Rgds.

Stephen Hobley March 28, 2011 at 9:03 pm

Davey – yes please do – I try to keep on top of things like that.

UPDATE: I think it might be a false positive, I have the minify plugin installed and there’s a whole slew of postings on the Avast Anti-virus forum about it being flagged as malware. The conclusion was that it’s not, and the anti-virus needed an update.

Davey T April 2, 2011 at 7:21 pm

Got a screen shot image. How can I send it to you.

It says –

Link Scanner Alert – Threat was Blocked!
Threat name – Exploit Blackhole Expolit Kit (type 1889)

Stephen Hobley April 2, 2011 at 8:36 pm

Thanks – I’ll contact my ISP about this.

I just checked my site with online tools and it came back as clean.

Stephen Hobley April 2, 2011 at 8:37 pm

Are you sure this is my site? – my IP isn’t – and I don’t have a Home/index.php file

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