BBC OBA/9 outside broadcast microphone amplifier, 1952, used by the BBC.
This unit (using EF37A valves) gives up to 90db gain and also has a line-up oscillator and a peak programme meter. The OBA/9 equipment was intended to replace the OBA/8 amplifier and its associated apparatus which the BBC had been using since shortly before WWII. The main advantages of the new equipment was that both size and weight had been reduced by nearly 50%. The OBA/9 units were still being used well into the late 1980s.