The Uax 12 was the first of the GPO’s range of standardized Uax’s. The standard range was the development of the experience that had been gained from the service of the earlier Uax’s, and incorporated the best features of all the previous designs. The main features of the standard range being the following:
The provision of standard tones (ie dial tone, ringing tone, NU tone, Busy tone)
The provision for 2-10 PBX groups
The provision for junction working (including discrimination on the junction routes for ordinary and coin box lines) by the use of relays sets, so calling equipment wasn’t used
The provision of multimetering to allow calls up to four unit fees to be dialed directly
The provision of a fault test number to allow the alarm conditions to be monitored remotely.
The UAX12 was designed to be a replacement for the UAX5, in as much as that subscribers multiple had capacity for the same amount of lines. As before the exchange was designed for installation in stages, the minium numbers of units being two the maximum (where designed) was five.
The numbering range of the Uax12 is 3 digits. The first digit dialed is a discriminator digit. Own exchange calls start with the digit 2, calls to the parent manual board are made by dialing 0, calls to the parent auto exchange are made by dialing 9. Single digit codes 6-8 are for use to junctions to adjacent exchanges (be they auto, manual or UAX). Levels 9 and 0 calls are routed from the ninth level, as the junctions on this level are combined, the extra impulse being used to differentiate for manual calls. This allows a saving in line plant for the parent junctions. The level 9 multiple is also slipped, which means that the first choice junction is different for a repetition call to the parent exchange (so if a junction goes faulty it doesn’t isolate the exchange). Any of the junctions that connect the Uax to its parent exchange can be used for trunk offering, and completion to Uax subs. Each junction that terminates on the parent exchange switchboard has two lamp signals, one for ordinary lines, and the other for coin box lines. Each junction has provision for multi-metering to be inserted, so that the correct fee is paid for the junction call, and also prevents dialling to exchanges out side the four-unit fee area. Metering is also effected automatically when the called sub answers, on calls dialed by the Uax sub to a sub on an automatic exchange. Overflow meters are provided (one per group of junctions, and one per group of selectors, ie one per group of A and B units).
Recently some photos have come to light that form part of the Peel-Conner/GEC archive, and below are shown two views of Brockton UAX12 when it was first installed (Probably in the early 1930's). I've left the images quite large as the detail in them is so good, especially the second shot of the equipment. Enjoy!