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 Post subject: I have a new project: a Tube Theremin
PostPosted: Mar Mon 26, 2012 4:43 pm 
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Location: Lyons, Kansas
Most people know that in the 1920's, RCA produced an electronic musical instrument called a Theremin. It was only a marginal success as only about 500 were produced. The few remaining are highly treasured, as they should be. A man named Moog had the skills to recreate a modern, working model of Lev Terman's invention named after him, the theremin.

The Moog Theremin has been accepted as a valid musical instrument that many people have learned to play. In its current manifestation it is a transistorized or micro-processorized musical instrument. A well-known advocate and producer of these theremins is Arther Harrison, who has a web-site where you can buy kits and finished instruments.

http://www.thereminworld.com/Keppinger-Theremins is another site that I found that promotes tube theremins in addition to the transistor models. Mark Keppinger developed a ten tube model that recreates and improves the sound of the original Terman theremin. He has kindly published the schematic and list of components of his model.

So my project is to build one. I got the two chasses and a set of coils:
Image

Image

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Mar Mon 26, 2012 5:33 pm 
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What a great project!

Note that the original RCA Theremins were built on a modified Radiola 60 chassis, using a modified Radiola 60 SPU (socket power unit). If you are planning to use the original tube lineup, you might well consider advertising in the Classifieds here for an old Radiola 60 chassis and power pack. One of these should cost you much less than the transformers alone for a reproduction Theremin. Note that RCA originally suggested that a 106 loudspeaker be used with their instruments. these are also relatively easy to find, althou they seldom turn up with their original tapestry grillecloth intact.

If you want a bit more power out of your Theremin, you could build it using a Radiola 66 chassis, which would allow the use of a UX245 output triode, rather than the UX 171a of the original design.

Note that a Radiola 60 chassis would also include all of the necessary audio frequency transformers

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Mar Mon 26, 2012 6:00 pm 
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Well, it will be a challenging project for me. Previously, I've only built 2 and 3 tube regenerative radios, although I have repaired all kinds of sets. But this will be a 10 tube oscillating instrument with a superaudio heterodyning circuit. It is not a recreation of the original theremin, but an improved updating of it. It uses octal tubes: 5Y3, several 6J5's, a 6H6, a couple of 6SN7's and a pair of 6V6's. These are all common, super cheap tubes and I already had them on stock. That's what I like about Mark Keppinger's design. Being able to buy the already bent and cut out chasses and the coils made this a must-do project. A "class" of about 20 individuals from around the world, under Mark Keppinger's direction, have just finished their instruments. They contributed last year to a yahoo forum as they built their sets. This forum was just recently moved to the theremin website. So I get the benefit of their imput into their forum as they built their instruments.

This should be of interest to anyone who has ever admired the RCA theremin. Being able to play the thing after it is built is a whole different question. :shock:

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Mar Mon 26, 2012 6:41 pm 
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If you listen to a master therminist considering that at a micro level the electrical circuit
formed between the whole body, especially the hands, and the chemical aura, (water-salt),
and the tone antenna , is looping back through their brain, it is just a small difference from singing.

Perhaps if Dr.Abrams' Oscilloclast had an audio stage his duck would have sung instead of quacking.

I wonder if you can play the thermin as well wearing surgical gloves?

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Mar Mon 26, 2012 9:46 pm 
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:D That is funny about the oscilloclasts and radioclasts of Dr.Abrams. Yes, had those things of sang he would have been considered a swan rather than a quacking duck of a charlatan. As best as I can explain of how bringing your hand close to the antenna causes a sound is that the antenna and your body consists of two plates of a capacitor. The person is the cathode and the antenna is the plate. Since you do not touch the antenna, wearing insulated gloves would not affect the process. The capacity between the person and antenna just increases as you get nearer. That brings the tone into the audible range. But I don't really know because I haven't even seen a real theremin yet. The first one I see will be the one I build.

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Mar Tue 27, 2012 1:01 am 
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I find this very interesting. Plese keep us informed of your progress.

Dave

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Mar Tue 27, 2012 4:12 am 
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mradiolab wrote:
Well, it will be a challenging project for me. Previously, I've only built 2 and 3 tube regenerative radios, although I have repaired all kinds of sets. But this will be a 10 tube oscillating instrument with a superaudio heterodyning circuit. It is not a recreation of the original theremin, but an improved updating of it. It uses octal tubes: 5Y3, several 6J5's, a 6H6, a couple of 6SN7's and a pair of 6V6's. These are all common, super cheap tubes and I already had them on stock. That's what I like about Mark Keppinger's design. Being able to buy the already bent and cut out chasses and the coils made this a must-do project. A "class" of about 20 individuals from around the world, under Mark Keppinger's direction, have just finished their instruments. They contributed last year to a yahoo forum as they built their sets. This forum was just recently moved to the theremin website. So I get the benefit of their imput into their forum as they built their instruments.

This should be of interest to anyone who has ever admired the RCA theremin. Being able to play the thing after it is built is a whole different question. :shock:


I have assisted people who have built copies of the RCA Theremin, and have also played on the Keppinger style units, and they say that they are practically two different instruments The original Expression system depended upon a UX-120, transconductance of which controlled the instrument's volume. The filament of the 120 was lighted by RF generated by a UX-171A oscillator. The volume of the unit depended on the voltage on the filament of 120, and so the expression had a bit of a time lag. The Keppinger circuit is much more sophisticated and rapid acting, and will make a more responsive instrument, but it will not play much like an RCA Theremin. Of course, this would not be a problem at all for someone who had not long been playing one of the old units, and may very well be an advantage.

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Mar Tue 27, 2012 7:38 am 
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mradiolab wrote:
. I got the two chasses and a set of coils:


Where did you source those? I didn't see them mentioned in the linked site.

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Mar Tue 27, 2012 8:02 am 
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After watching this http://youtu.be/rpMLYI0XG0A I want to make one as well though I don't the time or resources to do so. I've heard these before but I thought I was hearing some sort of synthesizer. Very cool. Can't wait to see what you do.


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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Mar Tue 27, 2012 3:09 pm 
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Quote:
Where did you source those? I didn't see them mentioned in the linked site.
http://www.therealcharleshobbs.com/theremincoils/
Both chassis and coils have been listed on eBay in the recent past.
xeric


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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Mar Tue 27, 2012 4:09 pm 
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Location: Lyons, Kansas
I was lucky enough to find both coils and chasses from Century_Art on ebay.

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0909172064

The seller had three sets of coils and chasses to sell. One auction was for the coils and another was for the chassis set. I bought one set of coils and one set of chasses. Then the auction ran out of time and disappeared. When he has time, I'm sure he will put the unsold sets back up. He says he is doing this to further the proliferation of Tube Theremins. I understand that the tone of a tube theremin is in a whole different class than the solid-state version.

For those who are interested in building a theremin, here is one caution: be leery of the Optical Theremins. They are a Tonal Only theremin, no volume control except for a potentiometer. And they sound like a motor boat. At least, mine did.

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Mar Wed 28, 2012 7:20 am 
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Thanks for the links.

I've decided to go ahead and build the Keppinger Theremin. I have ordered the coils, but it seems the chassis are not available at the moment?

The guy on eBay (who offered the coils) makes it pretty clear that he was clearing stock on a never-to-be-repeated basis.

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Mar Wed 28, 2012 9:44 pm 
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Actually, you've got what you need to start. The chasses, while nice to have them already made, can be constructed for probably less money than bought. For much less than the price of them, you can buy a greenlee punch and the flat steel from a hardware. You don't need them bent, but use them flat and fashon legs of some sort. Or some hardwares might have the means to make the bends. On one of the theremin websites it gives the exact dimensions and placement of all the holes. You only need one greenlee punch, a 1.13 inch, for the ten octal tube sockets. All the rest of the holes can be drilled. But it would be a major pain if you don't have a drill press.
Even after getting the chasses, I am having to ream out the holes for the tube sockets because the ceramic sockets I bought are just a hair larger around than the punched holes. Good luck on your Theremin, gtc!
I think Vitanola is telling us that no two theremins sound quite the same. I just hope mine will work when I get it done.

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Mar Thu 29, 2012 2:04 am 
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I'd prefer to fabricate the chassis out of aluminum. I've made chassis as a kid, however metalwork has never been my favorite pastime. I'll see if I can use my radio buddy network to get them made for me.

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Mar Thu 29, 2012 2:55 am 
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vitanola wrote:
Note that the original RCA Theremins were built on a modified Radiola 60 chassis, using a modified Radiola 60 SPU (socket power unit). If you are planning to use the original tube lineup, you might well consider advertising in the Classifieds here for an old Radiola 60 chassis and power pack. One of these should cost you much less than the transformers alone for a reproduction Theremin. Note that RCA originally suggested that a 106 loudspeaker be used with their instruments. these are also relatively easy to find, althou they seldom turn up with their original tapestry grillecloth intact.

If you want a bit more power out of your Theremin, you could build it using a Radiola 66 chassis, which would allow the use of a UX245 output triode, rather than the UX 171a of the original design.

Note that a Radiola 60 chassis would also include all of the necessary audio frequency transformers


What did he say?! :wink:

I have a Radiola 60/Brunswick 5NO that I bought strictly for the dial assembly (to fix another Radiola 60):

Image

Tap me if your interested in anything from it...

Regardless, good luck with the project! Will be fun to see you progress... 8)

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Mar Thu 29, 2012 5:02 am 
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Thanks, Tom, but the Kepplinger Theremin is entirely different than the 1920's RCA original theremin. The fact that it uses tubes and large oscillation coils it about all it has in common. If the RCA were a Model A, then the Kepplinger is a muscle car V8. In actual fact I think Kepplinger designed and built his first model in the mid 1990's.
Right now, I am getting my parts together. I have a junker 10 tube GE E105 that I cobbed the transformer out of. I've had the GE for probably 15 years and I know that I would never have done anything with it so I felt okay about taking the transformer. The transformer tests okay but I'll need to rewire it with new correctly color coded wires. The old ones are in bad shape. It also has a 12" electromagnetic speaker that I'm coveting for the Theremin.
The GE has a good tuner, with all the rf coils in good shape if anyone would need it. There were no knobs, however and the cabinet is in poor shape.

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Apr Mon 09, 2012 8:43 am 
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Well, I've ordered just about everything from everywhere.

Still mulling over the chassis: the guy who usually sells them on eBay hasn't replied to my email as yet (he showed some as unsold as of his last active listing) and I've yet to find somebody local who'll do it for me -- Easter is a bad time to contact people. I may end up doing them myself, although that's not my preferred option.

Putting this together is going to be fun. I haven't assembled a tube device from scratch since 1969 when I built a 40 watt guitar amp for a schoolmate.

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Apr Mon 09, 2012 11:03 pm 
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That sounds like you are making progress, gtc. It's good to have someone who is also building the same kind of theremin. Maybe we can help each other out as we run into problems. I have ordered the Transformer, Choke, and Output transformer from Radio Daze. In the meantime, I had to increase the diameter of the ten tube socket holes from 1.16" to 1.25" so my octal sockets that I had bought would fit. From looking at Chas. Hobb's photos on line, that didn't seem to be a problem for him or, apparently any of the others who have used those chasses. I guess it depends on what you buy for octal sockets. Anyway, I have the sockets installed and am waiting for my transformers and choke. Yes, this will be a fun project, but it may be a lengthy one also.

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Apr Tue 10, 2012 4:39 am 
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I haven't received my octal sockets yet, so I don't know their exact diameters. I ordered gold pin ceramics, simply because they were plentiful.

And there are 11 of them if you include the inter-chassis connector. :wink:

(unless you're using a 6 pin Amphenol or similar)

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 Post subject: Re: I have a new project: a Tube Theremin
PostPosted: Apr Wed 11, 2012 4:02 am 
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I forgot to order the eleventh one. But I have many old ceramic octal sockets. I'll use the best of one of those. While I'm waiting for my transformers and choke, I'm looking at pole lamps. I intend to put my speaker, which I already have, in a diamond shaped box at the top of about a 5 foot tall wooden pole. Or mount a square boxed speaker on a corner at the top of the pole.

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