Lincolnshire Heritage Telephone Exchange
Lincolnshire HeritageTelephone Exchange

LHTE: UAX 13

Our first UAX13 rack originally came from Winceby telephone exchange in Lincolnshire and We have it coded as Winceby on CNet.
Let me quickly talk you through the U13 rack.

At the bottom we have five relay cans which house the line relays, there are three relays per line.  Next to them we have a sixth relay can and this houses miscellaneous relays for alarms and such things.  Then on the right we have the allotters, these are uniselectors that prepare a circuit to a linefinder ready for the next subscriber who lifts their receiver.  Only one is used, the second is there as a backup

On the next row up we have two Control relay sets, these are associated with the allotters and again only one is in use at any time.  Next to them we have the first three linefinder, these hunt for the calling line when the subscriber lifts the receiver, each one of these is directly linked to a 1st selector (or group selector).  Above these we have five more linefinders making eight in total.

Then we have the meters, there are fifty subscribers to a single U13 ‘A’ rack and each has a meter here.  There are sometimes additional meters, usually overflow meters to count how many times the equipment was busy and a subscriber was unable to make or complete a call.

We then have two rows of group selectors, one each for the eight linefinders and two additional ones for connecting incoming junctions (these are missing on the early racks).  The group selectors return dial tone to the calling subscriber who can then commence dialling.   On receipt of the first digit dialled and they step vertically, then they rotate in to the bank to connect you to a free circuit on the level dialled.  If no circuit is free or the level is spare then engaged or nUmber Unobtainable  tone is returned.

Finally we have five final selectors, these are stepped by the last two digits of the number and it is here that the called line is tested to see if it is free, ringing or engaged tone is applied and the ringing current is passed to the called party.

We have two further racks deignated on CNet as Horsington exchange, one is identical to the above described rack, the other is an earlier rack in grey that did not have the two incoming junction group selectors.  I think I must point out that incoming junctions can access a rack on the first two levels of the linefinder, up to twenty in total.  Which is exactly the same amount of final selectors that can be accommodated across four ‘A’ racks.

In a UAX13 exchange there was one ‘C’ rack associated with the up to four ‘A’ rack, and this rack houses the connection between the equipment in the exchange and the exchange to the subscriber.  The ‘C’ rack and it’s associated ‘A’ racks provide up to two hundred lines and this was be doubled by adding a second ‘C’ rack and four more ‘A’ racks.

There were other racks that housed the junctions and and array of equipment, these being E, F, G and H, but nearly all the two motion selectors were on the ‘A’ racks, the only other rack to have such selectors was the ‘E’ rack that housed an extra levels of group selectors for larger exchanges.  
 
As said using levels 2,3,4,5 and 6 and adding additional C rack and four additional Anracks the exchange could be expanded to 400 lines. All other levels being reserved for connections to other exchanges, std and operator services.
 
If if you used the first group selector as a 1st selector, then directed the outlets of that selector to second group selectors, then four digit numbers became possible, thus the size of the exchange could be increased still further.
 

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