RCA Theremin Shock & Burn Hazards


Anyone attempting repair or dynamic adjustment of an RCA Theremin (electrically live), is at risk of burns and potentially fatal shocks. While the RCA Theremin is engineered to be safe under normal operating conditions, a number of factors can compromise this built-in safety.

There are numerous points in an RCA Theremin (as with any AC powered, high voltage device) that operate at potentially lethal voltage and current potentials.

A safety interlock switch that was designed to prevent tampering with the instrument when powered on, was standard equipment on all RCA Theremins when they left the factory. There are a number of factors such as replaced doors, bypassed interlock switch, insulation condition, etc., that can render this feature ineffectual.

Shock hazards can exist at the following locations:

  1. Wiring: There are a number of wires crisscrossing the components in the theremin, from the AC line cord in, to the AC accessory jack on the floor of the cabinet, the power switch wires and the wiring harness, all of which can present a shock hazard and risk of property damage if the insulation is deteriorated and/or missing.
  2. Power switch terminals.
  3. SPU terminals, especially if the steel cover plate and fiberboard insulator are missing.
  4. Safety interlock housing, if the insulation on the internal wiring has failed and a wire is in direct contact with the metal housing or internal moving parts.
  5. Speaker terminals (if powered up and safety interlock switches are missing or aren't functioning properly).
  6. Exposed solder lugs coils and components that are visible at the rear of the upper chassis (same interlock precaution applies as in item 5).

A fire hazard exists if exposed portions of power cord touch each other (in addition to tripping your home circuit breaker).

A burn hazard exists if you come in contact with hot vacuum tubes. This is especially true of the type 80 rectifier vacuum tube on the SPU (cabinet floor). The 71A tubes can also develop normal high temperatures.

Allow at least 5 to 10 minutes to cool, and unplug the instrument before opening the cabinet doors, to avoid contact with these hazardous parts and exposed shock hazards.

There is a great difference between knowing that a hazard exists, and always being aware that the hazard is present.