Can't Find Last Part to EW Theremin

Hello!

I'm currently looking to build a theremin. Due to other threads I've seen in this forum, I decided to build the Etherwave Theremin as detailed on the "Understanding, Customizing, and Hot-Rodding Your Etherwave Theremin" PDF I saw floating around.
Unfortunately, as I'm sure most of you know, it's quite old, and as of such, many of the recommended parts are not around anymore. That being said, I have been able to find parts with the same electrical component specifications, as detailed in the schematic, for all but one part:

I've gone around for a couple months looking for the part and even emailing manufacturers to check their stock, and have not yet found any within a reasonable budget (that's not to say they're not out there). Does anyone know where I might find this part or know of an idea for what I could do instead?

Thanks for any help!

Hey Shark,

If I was to start over today I might try these parts for the theremin oscillators.

The oscillators need distance between them so they do not interact with each other.

330pf Capacitor parallel with a variable 

Variable Capacitor  Use 50pf & 5pf in parallel for fine tuning

Coil 1-MH  You want a very low DC Resistance

Christophe S Becker
Old Temecula

The Theremin Phenomenon really is this basic.  Authentic Sound

There is special knowledge beyond parts seen to be more alive than just a deep fluty whistle.
.

Hi Sharkn8do,

after building my Etherwave in 2020, I wanted to make another one and introduce a few small modifications to the circuit. Toward the end of 2024, I tried contacting Coilcraft’s UK branch (Scotland/England) to ask about the SLOT TEN 5-10 variable inductors, and they managed to get me a few since they still had some in stock. I recommend writing to that branch as well to check if they still have any available.

Unfortunately, I’m currently stuck because I haven’t been able to find the fixed linearization inductors (for the volume and pitch sides), either from Hammond/Bourns or suitable replacements.

Do you have any ideas about that?
I hope you’ll be able to find the variable inductors you’re missing.
Good luck!

"Unfortunately, I’m currently stuck because I haven’t been able to find the fixed linearization inductors (for the volume and pitch sides), either from Hammond/Bourns or suitable replacements."  - Gianluca

This place might be able to help, but they want $12 a pop for pi-wound chokes, and not sure if they have the values the EW uses:

https://www.ctrengineeringinc.com/rf-chokes-and-inductors/

Evan got some custom wound by a Chinese outfit and they didn't cost too much.  They weren't ferrite core though so the Q was rather low.  I wish I'd bought a ton of Bourns back when they were still offering them.  Maybe one of us should build a coil winder and take this on as a project.

Hi Eric,
thank you for sharing the website. I’ll try to contact them to see if they can make the inductors like the original ones, or at least something similar. The price is quite high, and shipping them to Italy would be even more expensive.
I might also do as Evan did and buy a few from China to test them.
I wonder where Moog sourced the inductors used in the new 2022 Etherwave—maybe I’ll try to contact them.

Thanks again!

By the way, a few months ago I wrote to Hammond to ask if they still had any stock left somewhere in their warehouses of the 1535G/D/B inductor series. They replied that, actually, those famous coils were made by Bourns and not by them. Strange — I was convinced they were different. It’s not very clear to me… who knows how things really are.

Hey All,

There is no reason these inductors will not work. One or two can be wired to give you a series inductance of 30 MH which will resonate at 276khz the EWS variable pitch oscillator frequency. A resonating pitch antenna circuit is what gives ideal pitch field linearity. 5 pieces per order

Common Mode Inductor

Christophe S Becker
Old Temecula

Hi Oldtemecula,
in my research on this type of inductors, I’ve never been able to find the Q factor listed in the specifications, which should be quite high to ensure proper operation. However, it would indeed be worth testing to see whether other types of inductors might work or not.
Thanks for the suggestion!

"I might also do as Evan did and buy a few from China to test them.  I wonder where Moog sourced the inductors used in the new 2022 Etherwave—maybe I’ll try to contact them."  - Gianluca

I'm guessing the new EW and Claravox coils were China sourced.  If you do get some wound, make sure they're on a ferrite rod.

"By the way, a few months ago I wrote to Hammond to ask if they still had any stock left somewhere in their warehouses of the 1535G/D/B inductor series. They replied that, actually, those famous coils were made by Bourns and not by them. Strange — I was convinced they were different. It’s not very clear to me… who knows how things really are.

Oh, interesting!  IIRC I heard that Bourns's choke winding machines were accidentally junked.

"There is no reason these inductors will not work."  - oldtemecula

Can't say I've tried anything like these, but the self capacitance is probably rather high, so using them in place of the series RF chokes probably wouldn't work.  They might work in an LC oscillator where a large capacitance (>100pF) is in parallel, but even there they would likely have a lot of thermal drift because of the closed ferrite core, which is engineered more for field concentration and coil coupling rather than for a stable resonance frequency.  Miniaturization is a huge driver for modern components, but in general that isn't a good thing when targeting Theremin applications.

Very well, in the near future I’ll let you know something about it, and we’ll see if I can find a good and reasonably priced manufacturer in China.

Best regards.