RCA Theremin Infomation and Pictures

There have been a lot of questions on constructing RCA Theremin reproductions and for pictures of original parts. If you need information, parts, pictures, or sympathy concerning RCA's, ask here and everybody can use the data. The following pictures are available at members.tde.com/mmckeown/ by appending the following file names to this address.

CapsRblt2.jpg, DoorKnob.jpg, Cable.jpg, Front5.jpg, RtRearCornerBobs2.jpg, RtFrontCornerBobs.jpg, CapsRbld2.jpg, ChassisBord.jpg, ChassisTop.jpg, ChassisBot2.jpg, BackDone2.jpg, CabinetBeforBk.jpg, RCACapLabel.jpg, RCALabel.jpg, ChassisBot.jpg, and Top.jpg.

The file names are somewhat explanatory but cryptic. If anybody needs anything else post here and somebody will help you.

Mark (Dayfan)

Mark, Thanks for posting this (and also thanks for emailing some of them to me), but the urls aren't working for me. I also tried http://members.tde.com/mmckeown/Theremin/filename, like your previous photos, but that didn't work either.

I'd love to compile all the info of parts not included in your and Jeff's original drawings. Maybe here is a good place to start.

Mike

Mike,

Sorry but SOMEBODY forgot part of the address. Try this:
members.tde.com/mmckeown/thereminpics/filename
Should work a lot better. Also, even though I have posted this elsewhere on the site, I have a couple of original knobs. If someone wants to make copies send me your address and I will loan one to you. You could get some made at http://www.antiqueradioknobs.com/index.html
They may already have a mold (this is not a unique knob) or if the cost was divided up amongst the knob needers it shouldn't be too bad. I would like a pair myself. Check this site for other sources of old timey radio stuff http://www.stanwatkins.com/links.htm

Mark

The RCA GW-42 interstage audio transformers are about impossible to find. I have one and am looking for another. What I used in my replica are some I got from Antique Radio Supply in Tempe, AZ (Google) part number P-T156 equivalent to a Stancor A53-C. They actually work fine but may produce a slightly different timbre to the instrument. You can always change them if you find some originals.

I have posted pictures of the knobs as files RCAKnob1.jpg, 2, and 3 at the above site. I am also checking into getting some reproductions made. I can pass on at my cost or you can go to the source yourself if all is reasonable.

Mark

RCA Theremins were made by Westinghouse and GE. The serial numbers starting with 100 were made by one and 200 by the other. Manufacturers often used parts they had on hand so variations in parts are common in electronics made back then. These things were made by people who made radios using the same parts as radios (except the large coils) by the thousands. The antenna fits in the socket as a slip fit, the slits allow a little give so the antenna can fit snugly into the hole. The slits are necessary so the snug fit will result in a good connection between the antennae and the socket. Attached is a photo of an original antenna socket and wire connection. The wire from the coil is connected to a large lug on the socket. Note the two hexagonal nuts. The lug goes between the nuts, i.e. one nut holds the socket in the case and the other nut holds the lug on the socket/nut. Photo at:
members.tde.com/mmckeown/thereminpics/AntNut.jpg

Mark

If you are interested in using a modern amplifier or speaker with you RCA Theremin keep the following in mind. The high voltage (B+, a couple hundred volts) goes through the speaker winding. You need to not only match somewhat the impedance of the Theremin output to the amp input but also isolate the high voltage from the amp. You need a matching transformer. I would try an impedance of about 1-2000 ohms on the Theremin side to whatever the input impedance of the amp input is or the modern speaker you are driving. You may have a lot of AC hum because the Audio amp on the Theremin doesn't have the gain or amplify the hum like a modern amp does. You can pick up the audio before the Theremin's last audio stage off the grid through a capacitor and you will have a lot less hum. Your amp will more than make up for bypassing the last audio stage.

The "safety interlock" switches on the back of the RCA Theremin are fairly unique and I have not seen them anywhere else. Duplicating them would be very difficult but for those interested the following are pictures of an original set of switches and lever. The switch picture also includes the auxiliary power socket. The lever is fastened on the door and depresses the normally open switch lever to turn on the power when the door is closed. The switches are mounted on an inverted "u" shaped bracket that is fastened to the bottom of the cabinet.
members.tde.com/mmckeown/ThereminPics/doorswitchesPlug.jpg
members.tde.com/mmckeown/ThereminPics/SwitchLever.jpg

Mark:
Thanks for all the help you've provided for RCA builders like me. I am about to construct an adapter so that I can plug a 3Q4 into the V5 socket. I spoke with you much earlier about this, but all I know for sure is to tie 1, 3 and 4 together. I just don't know enough about tubes to know what else to do here. Here is what I think the correct mapping from 3q4 -> UX 120 should be:
1,3,4 -> F1
5 -> G
7 -> F2

But that isn't right because it leaves one of the 120s unused. Can you spell out the mapping you used in your replica construction?

Andy Baron was kind enough to sketch out the dimensions of his RCA chassis for me. I have made this picture available in an RCA Theremin album here:
http://picasaweb.google.com/pierce.krouse/RCATheremin/