Comments on: HTF Parts needed for a theremin.

Question: HTF Parts needed for a theremin.

KI6ILS — Sat, 31 May 2008 22:51:29 -0800

Where can I find a 50-300µh adjustable coil? I have searched the obvious sites; ie mouser, google, all electronics.

This is from a part list for a theremin from the 1967 Popular Electronics. The part list has a few htf parts like those coils. Here is a copy of the schematic. http://www.swtpc.com/mholley/PopularElectronics/Nov1967/PE_Nov_1967_pg30.jpg

By: TheOnlyCoolTim

TheOnlyCoolTim — Sat, 31 May 2008 23:28:50 -0800

I have searched the obvious sites; ie mouser, google, all electronics.

It's too late for me to go looking for odd things like adjustable inductors, but Digikey should be on your list of "obvious sites" for electronics parts if it's not already. Give them a look - they tend to be a bit more pricey but with top-notch selection and service.

By: action man bow-tie

action man bow-tie — Sun, 01 Jun 2008 00:03:06 -0800

Have you tried Octopart? It'll search many suppliers at once...

By: ShooBoo

ShooBoo — Sun, 01 Jun 2008 01:09:19 -0800

I happen to have coils in exactly that range. And they're yours for the asking (assuming I can find them).

Not coincidentally, they're in a theremin I built about 30 years ago in 8th grade from a kit (the exact same one you want to build). I never got it to work very well. It's output was so low that I had turn the volume way up on my amp to hear it resulting in way too much background noise.

I'm pretty sure I know where it is in my garage. Are you interested in it? I'd be happy send it to you for the price of shipping. You can contact me through MeFi mail.

(And I was pondering yesterday's question on decluttering and how much I need to do it. Getting rid of an old unused theremin that I've been keeping around for 30 years is a good start.)

By: zippy

zippy — Sun, 01 Jun 2008 01:22:23 -0800

action man, that was my thought too, but then I tried the search and I couldn't figure out how to construct a query to get 50µh - 300µh. Does Octopart do anything besides free text search? Because with electronic parts, if all you know is the spec, it's going to be hard to find the corresponding part.

By: FauxScot

FauxScot — Sun, 01 Jun 2008 05:32:51 -0800

Sometimes, you can use approximate parts. Digikey doesn't have any stock of 330's, but they have thousands of 390uH adjustable chokes by Toko in stock.

You can use smaller ones, too. They are a little more adjustable at the expense of range. if you absolutely have to have the low end value, you can stick a 50 uH in series with it (values add). Physical separation of the two by an inch or so is a good idea to if you do that.

You can also wind your own. Tedious, but an ARRL handbook will give you the formulas.

You can cannibalize old radio gear, too.... also old TV's.

(I once did some engineering work for Bob Moog, BTW. I had a lab full of theremins for a few month. Literally hundreds of them.)

By: fake

fake — Sun, 01 Jun 2008 06:51:08 -0800

ShooBoo, if KI6ILS doesn't take you up on that offer, I will. I'm working on a new album, and I'd be happy to pass it on to some other MeFite when I'm done.

By: overhauser

overhauser — Sun, 01 Jun 2008 09:15:33 -0800

Wow, what a fun project. I was wondering what to do with all the free time I have coming up this summer.

I couldn't find anyone making loopstick tunable inductors that cover such a broad frequency range anymore. However, this guy's theramin page has a workaround that uses a fixed frequency inductor with a tunable resistor coupled to a tunable capacitor.

Or, you could make your own inductors, if you want to be hard core about it.

By: overhauser

overhauser — Sun, 01 Jun 2008 21:54:26 -0800

Pun intended, of course.