BBC OB Type 9 amplifier

EVE BBC OBA 9 in situ

The OBA/9 system evolved in the 1950s to replace OBA/8, with a smaller footprint and expanded facilities to meet the demands of outside broadcast engineers as the needs of broadcast expanded.

OBA 9 close up

The whole system was designed to be ‘portable’ of a fashion; consisting of an MX/29 passive mixer, OBA/9 valved amplifiers with high gain and power supply, along with monitoring amplifier and distribution facilities. Ancillary items included a loudspeaker LSu/11 and communication units CMU/9 and CMU/10





One thought on “BBC OB Type 9 amplifier

  1. Mx18 passive mixers were not constant impedance like type a and b faders they purely attenuated the microphone feeds into a common bus which had an unknown low impedance feed for the 70 db gain of the oba 9 amplifier. That way they could be cascaded together. The final mix had an unknown source impedance which did not matter to the oba9 amplifier,


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