BBC MX/29 passive mixer, 1952, for use with the OBA/9 outside broadcast amplifer. Four-channel unit with variable impendance balanced series faders. For each channel there are two input jacks; one for a ribbon microphone (connects straight to fader) and the other for a moving coil microphone (connects to fader using a 30/300 ohm transformer). Part of a complete OBA/9 trolley (TRL/1) comprising 6 units, including cable. Note the serial numbers of the units - most of this rack comprises the units used in the original BBC service trial (two sets were used). OBA/9 units were still being used well into the late 1980s. BBC OBA/9 Outside Broadcasting unit and associated equipment 1952
