Interesting hand me down from my father

Hi, I'm new to the forum and believe I have an interesting Theremin that was given to me today by my father.  IT's a Moog model 201 SN:5425. 

I remember playing with this as a child about 30 years or so ago.  From what I've read and seen so far, it's missing the volume control plate.  I'm hoping that's the reason it's not working quite properly.  It does power up properly and there is some oscilation detectable, but it's mostly just a rather loud static with no control over the volume.

Is it possible to just use a piece of brass plate between the posts on the volume side to see if that's the problem?  I'm very interested in getting this working again.  I have some experience working with vintage guitar tube amps, so this is pretty intriguing!

Any help or input would be greatly appreciated!

Thanks,

Brian

Sody54@gmail.com

Brian Sody Sodergren on Facebook

Whoa! nice.    if it is missing the brass volume plate, that would be a good place to start.   Look inside, and everything 'looks' intact- specifically the connector between the circuit and where the volume plate mounts.  You may be able to find a schematic online- check the Moog Archives.

The static might be a concern- I would recon that without a volume antenna there would be just silence(=full mute).  

this has tubes right?   Those and capacitors are the next likely suspects.

good luck!

Hello Brian,

I have never registered with Facebook but I think you are near Portland, Or. USA

Chobbs is right so I will add a little more to your exploration. My first test with a non-working theremin is to set an analog AM Radio next to it and tune across the dial to pick up the fundamental freq or a harmonic. You will find the two pitch oscillators if working and possibly the volume oscillator if it uses one. This will be a blank spot in the static or a whistle. This test bypasses a non-working volume control.

Digital radios do not work for this test if there is no heterodyne whistle yet.

Capacitors are an issue when really old as Chobbs stated but the component that bothers me when I design is the Potentiometers. Unused these gum up sitting in the closet. Use the proper Pot cleaner DeoxIT and don't use WD-40 as that will gum them up more and destroy them long term.

Try to properly restore the volume plate so it looks original.

You have a very nice collectable

Christopher

Full details (Construction article in Radio and Television News, 1954) can be found here:

http://moogarchives.com/therem00.htm

Lovely instrument!  When you get it working (not if! ;-) please record some samples of the sounds with the quint and octave switches in thier 4 different combinations and post them online - PLEASE! ;-)

Best of luck!

Fred.

Hello Brian,

I have never registered with Facebook but I think you are near Portland, Or. USA

Chobbs is right so I will add a little more to your exploration. My first test with a non-working theremin is to set an analog AM Radio next to it and tune across the dial to pick up the fundamental freq or a harmonic. You will find the two pitch oscillators if working and possibly the volume oscillator if it uses one. This will be a blank spot in the static or a whistle. This test bypasses a non-working volume control.

Digital radios do not work for this test if there is no heterodyne whistle yet.

Capacitors are an issue when really old as Chobbs stated but the component that bothers me when I design is the Potentiometers. Unused these gum up sitting in the closet. Use the proper Pot cleaner DeoxIT and don't use WD-40 as that will gum them up more and destroy them long term.

Try to properly restore the volume plate so it looks original.

You have a very nice collectable

Christopher

Christopher, Thanks for the info.  I'll give the AM radio a try and see what comes of it.  I use nothing but DeOxit on any of my equipment.  Any ideas on where (or even if) a stock volume plate can be sourced?  If not, any suggestions on where to find pictures of one so that I can make one that's as close to stock as possible?  Going to open it up this evening and see what's what inside.  It would be nice to find a disconnected wire or something, but I'm not holding my breath! lol

Thanks

Brian

Just call Moog and ask for a 'stock volume plate for a 201'- they'll be happy to help you out!

seriously tho...  your on your own, but it is probably just a rectangular piece of brass.    are there any marks on the cabinet that indicate the dimension or you remember the approximate size?    Or best yet, read the moog article that fred posted.  the dimensions and thickness of the plate should be listed there.

Should also have a schematic and pictures so you can check and make sure everything is connected.

The radio trick is cool, but can be kinda frustrating.   A $40 ebay/amazon  Multimeter with a freq counter function is far easier to check if an oscillator is oscillating and at what freq.  And you can check each one individually.  If you dont have a multimeter, get one now.

If youve messed with tube amps and have some electronics experience, this shouldnt be too hard of a project just take your time and dont do any damage.  its probably all point to point and easier to replace components.     Try to find a local place to test the tubes

Just call Moog and ask for a 'stock volume plate for a 201'- they'll be happy to help you out!

seriously tho...  your on your own, but it is probably just a rectangular piece of brass.    are there any marks on the cabinet that indicate the dimension or you remember the approximate size?    Or best yet, read the moog article that fred posted.  the dimensions and thickness of the plate should be listed there.

Should also have a schematic and pictures so you can check and make sure everything is connected.

The radio trick is cool, but can be kinda frustrating.   A $40 ebay/amazon  Multimeter with a freq counter function is far easier to check if an oscillator is oscillating and at what freq.  And you can check each one individually.  If you dont have a multimeter, get one now.

If youve messed with tube amps and have some electronics experience, this shouldnt be too hard of a project just take your time and dont do any damage.  its probably all point to point and easier to replace components.     Try to find a local place to test the tubes

I checked out the article earlier today.  Haven't had a chance to read all the way though it yet.  I'll get ou tmy trusty Fluke multimeter and get my buddy over here with his scope.  We'll get this figured out.  I've got access to a tube tester as well, so hopefully this won't be too big a job! :)

The full details on the plate are available in the Construction article in Radio and Television News, 1954 which can be found here:

http://moogarchives.com/therem00.htm

This was a DIY project in 1954! - Everything you need to know, in full detail, is in that article!

Fred.

 "The radio trick is cool, but can be kinda frustrating.   A $40 ebay/amazon  Multimeter with a freq counter function is far easier to check if an oscillator is oscillating and at what freq."

Not quite that easy! - IMO, If you load an oscillator with a multimeter, its frequency can change - You need a good frequency counter with both antenna and probe options - see http://www.thereminworld.com/Forums/T/28822/yaege-fc-1-frequency-counter-question.