BBC TS/10 Tone Source, 1960. Rack-mounted tone source (valve) 20Hz to 20KHz. Uses a Wien-Bridge oscillator with its frequency set by the large slow motion dial on the left. The meter in the middle was used to calibrate the output level and measure supply volts. The big knob on the right controlled the output attenuator, in conjunction with the 3-way lever switch underneath.

TS/10 was one of the rack-mounted components used in BBC's A.C. Test Bay AC/55, a 19-inch bay of equipment for the audio-frequency testing of sound apparatus and the audio-frequency and direct current testing of lines. At small centres where the full facilites were not required the bay was supplied partially equipped as necessary to suit the requirements of the particular station.