EM Theremin Replacement Parts

Posted: 2/4/2020 7:26:46 PM
JordanCharest

Joined: 2/4/2020

Hi!

I am currently building the EM Theremin using Moog's schematics. I'm having trouble finding some parts and/or replacement parts for the inductors:

L5, L6: 100 uH, hi-Q, variable inductor (Toko RWRS-T1015Z)
L11: 68 uH, hi-Q, variable inductor (Toko 154ANS-T1019Z)

Can't find variable inductors with those inductances anywhere. Tried a lot of websites, visited a few local stores (which don't even sell variable inductors at all anymore), nothing. Only exception is on Mouser.ca, where I can order them in packs of 250, so not ideal.

L9, L10: 5 mH, 3-section, RF choke (J. W. Miller no.6304)

Found the other inductors, but I'm struggling to find a replacement part with the same inductance as this one.

If anyone knows of replacement parts or equivalents for those, any help would be greatly appreciated.

EDIT: Forgot to mention, but I'm in Canada, so I have to ship the parts there!

Thank you!

Posted: 2/5/2020 12:01:49 PM
pitts8rh

From: Minnesota USA

Joined: 11/27/2015

"I am currently building the EM Theremin using Moog's schematics. I'm having trouble finding some parts and/or replacement parts for the inductors" - JordanCharest

There have been several changes to the Etherwave main board design compared with the schematic that you are probably working with.  The variable inductors are now Coilcraft SLOT TEN-5-10, and a few other component values have been changed and some inductors eliminated.  Here is a copy of an Updated Etherwave Schematic that I modified a few years ago based on the then current Moog board design. Unfortunately the part numbers are not annotated, but the component values and reference designators are correct.

You said later in you message that you found the other inductors (all of them?) except for the 5mH Millers.  If you really have everything except those, including the variables, and are that close to having everything you need, contact me by PM and I may be able to help.

Otherwise, I don't ever want to be the one to discourage the enthusiasm of a building project, but I should at least let you know that on two separate occasions I have been able to buy fully tested factory main boards and optional CV boards (if you want to make an EW Plus) for under $70 and $80 respectively. It would be difficult to build either of these for that price, and the difficulty of getting a homebuilt theremin tuned up and functional should not be underestimated. Each time the people I spoke with at Moog were very friendly and helpful, and seemed to have no problem selling these assemblies.  My last order was probably 2 years ago, so prices and/or policies may have changed, but you could always try.

Posted: 2/5/2020 10:08:13 PM
JordanCharest

Joined: 2/4/2020

"There have been several changes to the Etherwave main board design compared with the schematic that you are probably working with.  The variable inductors are now Coilcraft SLOT TEN-5-10...

Thanks a lot for the reply!

I should have been clearer, I have not found the variable inductors yet, though I'll take a look at the Coilcrafts and I'll let you know if I have any luck. Besides, I just realized I had the wrong inductors for L1-L4, L7-L8 as well. Oh well.

I gotta admit that it's more for the thrill of building it that I'm doing this project, so I don't really mind if the results are less than optimal  Thanks a lot for the tips!

Posted: 2/6/2020 10:30:34 AM
pitts8rh

From: Minnesota USA

Joined: 11/27/2015

"I gotta admit that it's more for the thrill of building it that I'm doing this project, so I don't really mind if the results are less than optimal."

That is understandable.  You might look into some YouTube videos on winding your own RF inductors as a substitute for the Miller pi-wound coils. This would be an adventure in itself but if you have some test gear (a basic oscilloscope is almost a necessity for any theremin work) you can get there.  Or do a search for the Moog Melodia which was a predecessor to the Etherwave.  It has more detailed DIY information on hand-winding your own coils, although the coil forms and germanium transistors used in the Melodia are rare but still available.

It's almost easier to learn about theremins by starting with something that is working and doing your experimenting from there.  The Etherwave is a very good basic instrument but as you have seen parts availability for scratch-building is a problem ( I don't know if the factory has bought an end-of-life supply of the discontinued inductors or if they have their own special supplier).  There are always the Theremax and Jaycar theremins available in kit form, and the schematics are available for both of those online.  These use the much more widely available (for now, anyway) AM radio IF and OSC variable inductors that can usually be found for like a buck apiece. They both have some support resources for getting the kits operational but you don't really see many demonstrations of the finished products, for whatever reason.

Searching for topics here on Theremin World can turn up a huge amount of information from past discussions, too.  The Element14 forums have some theremin information buried in the archives as well.

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