B13's desk was new when the photos on this page were taken in 1971 and was a stereo version of the marque. The modules in the left foreground are stereo processing (width, offset, balance). The right hand wing includes RSAs and OS modules.
The main module is on the left, then comes the echo module which includes control of a remote echo plate. The three stereo channels are followed by the monitoring module and eight mono channels. Controls on the stereo channels are routing (see 3E page), gain pre-sets, echo mixture, foldback, cut key, fader and prefade. Mono channels add a pan pot and omit the cut key.
The bay is visible in the background. There are further jackfields either side of the desk - the main routing and the insert jackfield. BBC desks still did not have EQ on every channel - the RSAs (eq modules) had to be plugged into the channels as required.