1961 Electronics Illustrated tube theremin question

Hi there,

I've been looking with interest at the build article by Craig Hanson about the tube theremin described in the 1961 issue of Electronics Illustrated and I have a few questions about some of the components.

First, the 500kHz crystal - the article says that crystals with frequencies around 26 or 27MHz will work (which is great, since 500kHz crystals are like hen's teeth). A quick search on Mouser shows that most of these crystals have a tolerance of around 30ppm, is that OK?

Second, the article calls for a power transformer with 240-0-240 secondary. Craig uses a Hammond 270ax, which is 250-0-250. Is it OK to go a little under as well. I have a transformer handy that has a 230V secondary. The other consideration is that the transformer I have has no centre tap on the secondary, so if 230V unregulated is OK will it be OK to use a hybrid design (about half way down the page) with some rectifier diodes or just substitute a bridge rectifier for the rectifier valve?

Third, the BOM calls for a couple of porcelain feed-through insulators. Do they have to be porcelain? It'd be nice if I could find an reasonable substitute from Mouser or AES, to keep minimise the number of places I order from. Something like this looks OK to me - it's rated for 15A and 2.85kV

Thanks, Patrick

Patrick why did you choose that particular theremin, did it create a sound you like?

Why build something that many of the parts have faded into history?

What country are you in, some people prefer to help home boys, only lurk and never post but they are out there.

There is a private message indicator in the upper right corner you should keep an eye on as your email address is only known to you.

You ask for advice and give no hint of a skill level, a vacuum tube theremin could burn you or drop you to the floor. LOL

I do wish you luck.

Christopher

Edit: I looked further and the builder did not furnish a single sound byte, that is the most obvious indicator he has tremendous effort into his build but it is all show and no go. Are you sure this is the path of theremin punishment you want to choose?

Hi Christopher, thanks for the response. I must admit that I'm guilty of thinking more about the build than the sound - as you said, a bit of a no-no for theremins :)

From the way that the article was written, I would guess that Chris was more interested in the build aspect, but the lack of sound samples is definitely a bummer.

I was attracted to the build because I'm getting into building tube guitar amps, so the idea of a tube theremin was interesting. That and the fact that this build doesn't require any custom coil winding. As far as skill level goes, I have good skill with a soldering iron and some experinence with audio electronics projects - I built half a dozen effects pedals earlier this year with success And I've built projects that Require mains wiring, too (a plasma globe that was pretty potent). I'm in the USA at the moment (Davis, California), but moving back to Australia at the end of the year.

I'll approach the project as a side interest - I like the sound of the Burns theremins and they have a good reputation, so that'll be my main instrument and the tube project will be for fun :)

Patrick in Davis where hwy 5 divides off to a place where children wear flowers in their hair. In a worldly perspective we are neighbors. I might be saving you from yourself with all respect by mentioning the following.

In my research I was never able to figure what the ideal sound of a theremin should be, I do have a tube sound using tube/valves but that was a gift for me in why it comes about. I am sure it would sound better if someone could play this sound. Notice the lack of a reverb band-aid.

Tubes and transistors each have their own uniqueness. After many years I prefer solid state construction because it has more flexibility. There is something unique that can be done using a tube as heard above that can't be done with a transistor, then there is much more that can't be done with a tube.

In the world of theremin only a handful demonstrate or walk their talk. The webpage you mention he is not walking. To keep from getting mugged I keep a lot of my work private. Visiting my public pages might be a good start for you. The theremin has many paths.

Sometimes something clicks in my head and I think I should tell a person more, but more often I can tell when they are not ready.

Christopher

Yup, that's the place - we're certainly closer now than when I move back to Oz :)

I liked your sound clip, thanks for posting that. A theremin that inherently sounds good is definitely a priority for me, but the "ideal sound" is less of a quest for me - my playing's the limiting factor with any theremin, rather than the quality of the sound.

I've seen your website before, there are some fascinating ideas. Props for designing a theremin from scratch, too, I'm confident in my construction ability but design is way beyond me!

The tube vs. solid state differences would be interesting. Many consider tubes to be a requirement for a "proper" guitar amp, because of the inherent distortion and compression characteristics when the tubes are pushed. That wouldn't be a goal for a theremin, though, since the tubes wouldn't be pushed that hard and distortion certainly isn't desirable. Eventually, I'll build one of each and compare :)

Hey Christopher - who the frack are you? If i said it works great, then IT WORKS GREAT. No one needs your pretentious speculation as to the motives or accomplishments of others. You said two things that I agree with though - a) "To keep from getting mugged I keep a lot of my work private." Guess what - me too! Funny that some goatee-sporting goof like you is the one doing the mugging.  (Truth be known, while I am very happy with the sound of my Theremin, I have also confirmed the findings of nearly everyone else who has tried - it is extremely difficult to "play" pleasingly, and I simply saw no need to demonstrate my incompetence as a performer.) And b) "The theremin has many paths." Sure does - so what makes my path less valid than yours?

For the record, I built what I built for a variety of reasons, none of them having to do with Carnegie Hall-worthy sonic results, although the machine I built sounds significantly better than any solid state version I've ever heard in person, probably a total of a dozen or so. I had personal goals, namely to learn more about practical tube circuit construction, to pay homage to an earlier era of home electronic experimentation, and to have fun. All of these goals were achieved, "and" it sounds great. That is my walk, and I am most certainly walking it. Can't imagine why you or anyone else would have a problem with it unless you've got a serious insecurity thing going on.

Craig

Hello Craig,

You are a lot of fun, you will do just fine. I enjoy everyone's design as anyone with demonstrated theremin success knows how difficult it is to develop a musical sound. Now to figure out the love between us?

The other Christopher

Well played. I confess to being new here and was somewhat offended. It has now passed.

Gentlemen! please pardon my ignorance, I am a carpenter and musician in Wilmington NC, and have fallen in love with the theremin so much so that I would like to build one. I know enough to be safe, however my electrical experience only exists with engines, houses, and robots I make to do tasks like opening beer. I hope someone can help me with a few questions in relation to oscillator coils and the electrolytic can that was called for in the diagram. I have been having trouble finding an affordable P-C70 and the miller 70 is a ghost. I was naively wondering if any adjustable 4 pin oscillator coil would work as a decent substitute, such as the miller 71. If not I was hoping I could get some intel on where to find the 2 coils and if you feel so inclined, the transformer is something I cant seem to locate either. My electrolytic can arrived in the mail with a compromised seal and i was wondering if I could just use 3 separate capacitors in its place. 30Mf, 20Mf, 20Mf, and if so would I need to make any special modification to the circuit to accomidate them. I thank you for our patience if you've read all of that. 
Logan