With the start of stereo transmissions some modifications were made to Egton 3's desk to allow it to take over the B4 role, but with the ability to play stereo discs. This work was probably quite limited, with grams modified, a stereo channel on the desk and stereo main fader and output amps. The existing faders were used. Type A faders were balanced bridged-T types, and had three 'tracks' (actually they consisted of a wiper running over studs with resistors wired between them). Two of the tracks were used to make an unbalanced stereo fader. No stereo metering was provided, the existing PPM could be switched between the A or B legs or to A+B - the mono sum of the left and right channels.
Further work was carried out in 1977/8 to produce the result shown in these pictures.
This time the original faders were replaced with the type used as group faders on Type B desks, which could handle the two channels without modification. The photos suggest that three channels were stereo, with balance controls (below the faders) giving about 5db swing left or right. These were used to balance recordings which appeared to have an offset. The remaining channels were mono and lacked pan pots, their outputs appearing to the centre of the stereo image.
A new wing panel was constructed to the left of the desk. The top row contains four mono RSAs (Response Selection Amplifiers, i.e. EQ) and a stereo RSA. The next module may have been part of the limiter system and then come the two mono limiters (of the type used in Type D equipment). Below are six mic amps, supplied by Calrec and a final mystery module!
For the 1970s rebuild a stereo PPM was provided, as well as the original mono one. The white-faced meter to the extreme right of the desk was part of the echo-plate installation. It indicated the reverberation time setting, which was set by the buttons either side of the meter.