Part of the OBA/9, the MX/29 incorporated 4 passive constant impedance attenuators.
Utilised across the BBC during the Fifties, the one in the photo below was the original mixer for the Radio One Roadshow which launched in 1967.
The Manchester Playhouse, home to the Northern Dance Orchestra, utilised an array of BBC OB equipment, including no less than 5 x MX/29s as seen on the RHS of the picture below
Additional items to the OBA/9 trolley were these communication units for lamp signalling between the operator and various microphone points.
The CMU/10 also provided for a P.P.M. meter which was powered off the OBA/9 rig.
Not currently in use, but looking forward to getting these lit up like a Christmas tree.
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.
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