RCA Theremin Identification & Serial Numbers

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Serial Number & Cabinet Number locations

Serial Number

The six digit serial number is stamped in one of two places on the brown metal chassis depending on whether the theremin was made by Westinghouse or General Electric subcontractors. Westinghouse serial numbers begin with 200 and are located in front of the UY-227 vacuum tube socket behind the taller coil form. GE serial numbers begin with 100 and are located in front of the middle UY-227 vacuum tube socket in very small numbers. The minuscule size of the GE number embossing and its apparent hand-stamped qualities can make it very difficult to read. Good lighting and magnification can help avoid errors. We encourage the submission of photographs of serial numbers to our registry.

RCA Theremin, bird's eye view, with doors open and chassis board partially removed.

RCA Theremin, bird's eye view, with doors open and chassis board partially removed. The serial number will appear in only one of these two locations. Westinghouse is on the left, GE in the center.

If the theremin is a Westinghouse, it may be easier to read the serial number behind the tall coil if you slide the chassis board out partially. Remove the two screws that secure the outer ends of the board (if present), and mind the cables. To avoid possible damage, do not slide the shelf more than needed to view the serial number; approximately four inches should be sufficient. Note that there are no stops to prevent dropping or tipping the shelf if it is drawn out too far.

Cabinet Number

The cabinet number is located under the back doors of the cabinet. It is stamped into the wood on both doors. It should be between 1 and 500, but may be higher.

RCA Theremin, worm's eye view, with doors open and chassis board partially removed.

RCA Theremin, worm's eye view, with doors open and chassis board partially removed.

Differences between General Electric & Westinghouse Theremins

RCA subcontracted the manufacturing of the theremin to their two primary U.S. suppliers: General Electric, located in Schenectady, New York, and Westinghouse, located in Springfield, Massachusetts. GE built 300 Theremins, and Westinghouse made 200. Since they were made in different factories, there exist a few distinguishing features that make identifying the subcontractor easy. These are listed below.

It should be noted that only the chassis serial number is the most trusted proof of factory origin, since replacements and restorations over the years may have obscured some of the normal identifying features.

The chassis serial number will help us identify the RCA subcontractor as well as a particular theremin's sequence in the production. The cabinet number, which is stamped into the bottom of each door, is unrelated to the factory that produced the working parts of the instrument. When adding your theremin to the Registry, the chassis serial number is required.

General Electric
100XXX serials
Serial stamped in front of “V4” 227
Black phenolic 3 inch coil forms
Ceramic trimmers mounted with screw
Volume trimmer mounted “inside” of chassis
Chassis board screwed from sides, pocketed
SPU labels: “UX-280” and “110-V” in white
Large coil mounting nuts: 1/4″ width.
Volume coil secondary winding 4+5/8″ from bottom of coil
Hexagonal antenna nuts
Gold label on upper right corner of inside of door
Red RCA paper label on 2 MFD capacitors
Westinghouse
200XXX serials
Serial stamped in front of “V1” 227
Brown phenolic 3 inch coil forms
Ceramic trimmers riveted to metal strip
Volume trimmer mounted “outside” of chassis
Chassis board screwed from top
SPU labels: “UX-280” “120 V” and “110 V” stamped
Large coil mounting nuts: 5/16″ width
Volume coil secondary winding 5″ from bottom of coil
Octagonal antenna nuts
Gold label centered at top of inside of door
No red RCA paper label on 2 MFD capacitors
The placement of the white ceramic volume trimmers on GE and Westinghouse Theremins, illustrating the difference.

The placement of the white ceramic volume trimmers on GE (left) and Westinghouse (right) RCA Theremins.