Leaving aside the left hand column of panels for the moment, there were six channels handling remote sources. The three panels of push buttons and six select keys at the top allowed any one of 200 sources to be selected to each channel, although not all of these were relevant to the work of continuity. It would have been perfectly possible to have one set of push buttons and six select keys but the system used had built-in redundancy to allow for mechanical failure of the push buttons. In practice, though, they were extremely reliable. The third row of panels carry the faders and red light signal keys for the six channels.
Below these faders are the indicator windows to show what source has been selected to a channel together with adjacent 'pre-fade listen' keys ('pre-hear' is the name now more commonly used). Beneath the indicator windows are four keys and a lamp. The lamp together with a common buzzer indicated a call from the source that could be answered by the operator on one of two bus bars A or B. A second key allowed the operator to ring the source or to recall EMX (the Engineering Manual Exchange in the Control Room) should the source need to speak to control room. The remaining two keys fed either clean feed or cue programme to the source via its cue line or control line if these were available; in fact this facility was rarely used.
Also on this bottom row of panels are keys to ring and answer EMX. There were two EMX telephone lines whose function depended on whether the suite was working as a continuity or as a production mixer. EMX1 appeared on SB EMX when the suite was serving a network under the name of that network (Home, Light, Third). When the suite was not serving a network EMX1 appeared on OB EMX under the name of the Continuity (1, 2, 3, 4). EMX2 had no function when the suite was serving a network but a control line could be plugged to it for special purposes such as a control line from Light Con to Green Con in Bush House. When not serving a network, EMX2 was the control line associated with the suite in the source multiple just like any other studio. The remaining two keys are the operator's answer key switchable to the A or B bus bar and a similar key to switch the announcer's telephone to either bus bar. Thus the operator and announcer could hold separate conversations with two different sources or both could have a 'conference' call to one or a number of sources. These comprehensive arrangements were clearly intended for 'production mixer' use; routine con operation made little or no use of them.
Moving back to the second row of panels and starting with the second from the left, there is an STC 4021 'apple and biscuit' mic which was used for talkback to the studio and for the technical intercom. The large white knob was the main gain control with a pull type bypass switch below it that replaced the control with an 18dB pad. The two small black knobs were pre-set level controls on the mic and the gram outputs from the studio with a studio prefade key between them. The next panel to the right carried the main and prefade PPMs both of which could be 'slugged' by toggle switches at their upper right. At their lower right is the electrical zero adjustment control. The two keys were an LS dim key and Desk out/Check Receiver + PFL/Check Receiver. The last panel to the right carries the check receiver indicators and a key which would lock the output to either the AM or FM receiver as opposed to the normal sequential 20 seconds each switching. AM monitoring was eventually officially abandoned as the quality change from FM was so disturbing. This panel also carried the amplifier changeover pull switches and the announcer's main gain control bypass pull switch together with lamps to indicate announcer's Mic On, Fader Up, Fader in circuit and Rehearsal. The auto GTS (Greenwich Time Signal - the "pips") key and indicator lamps were on the extreme right but the lamps were a bit too small to warn the operator if the automatic system had selected a GTS that was not required. The three black knobs from left to right were the loudspeaker volume control, a cubicle ring main selector whose output could be heard by operating the key to its right and a cue programme selector for feeding cue programme to the cue and control lines. The three keys to the left of the selectors were a Tone Key, Channel 6 signalling transfer which transferred red light signalling on channel six to the announcer which I doubt was ever used and a key to enable or cut talkback from the announcer to all clean feeds. It is extraordinary that the operator had no means whatsoever of using talkback to the cue or control lines although he could talk on the telephone handset to a control line.
Returning to the first column of panels. At the top were the single Transmitter Repeat Lamps. This facility is described in the section about the announcer's desk. The locking key is for the continuity interchange system. If a network needed to change to another con, both faded up the same programme and did a PPM check. Then both operated their con interchange enable keys. In the control room, the operator on the SB position checked that the spare con did have the same prog on its output and then operated the key that switched it into network. Nothing actually happened until the key for the con to be vacated was operated up. When this was done everything was transferred to the spare con - check receivers, C/R intercom, indicators outside the con doors and in PABX etc, etc. There was no danger of howl round as the relays involved were arranged so that it was impossible for one to operate before the other had released and in addition they were mechanically latched by a bowed spring so that they did not depend on the 50v supply to stay operated. After the interchange had been done both cons released their keys.
The other three panels were mainly intended for an auxiliary operator although Continuity soon became a one-man job (nobody spoke of one-person jobs in the 1960s). The auxiliary operator had a PPM fed by aux. prefade keys. The key to the left of the PPM fed the aux. ops headphones with Desk Out or Check Rx + PFL. The 15 keys to the right were the technical intercom. The speak/listen/off key was to the left of the adjacent mic.
The third panel carried the tape fader with its bypass pull switch and, on the left, the locking keys controlling the tape machines. With the keys as shown in the picture, machines 1 and 2 are selected to the repro busbar and machine 1 is started on remote. Only two machines could be selected to the repro bus at a time. The first two that were selected locked out selection of the third. The keys in the middle of this panel were aux. prefade. The bottom panel gave the auxiliary operator access to all the telephone facilities available to the main operator but with the addition of a means of sending TIM (the speaking clock) to any control line for time checks.
It was intended that the continuities would be equipped with EMI TR/90 tape machines but they entered service with Leevers-Rich machines. These were later replaced with Studer C37s.