Medstead
The opening of the line to Medstead saw a small GEC PAX being placed in service in 1983. In very cramped conditions there were 2 cabinets, one for final selectors, line finders, junction relay sets and common equipment, the other cabinet contained group selectors.
Numbers were in the range 51XX.
Space was so limited that the equipment required for the linked number working was installed at Ropley, an overhead pole route connected this station to Ropley.
Linked number working arrangements comprised as follows -
Calls to an Alresford extension 22XX or Ropley extension 43XX were routed to common relay sets connected via junctions to Ropley exchange.
The relay set could detect if it had be seized via level 2 or 4, subsequent digits were sent to the distant end.
Call barring was achieved by the examining the second digit dialled, if the call was via level 2 only a second digit of 2 was permitted and via level 4 only a second digit of 3, all other combinations would result in the caller getting unobtainable tone and then force released.
At Ropley the junction terminated on an incoming relay set and the digits were stored on an electronic regenerator; the first incoming digit received was checked. If 3 it was a call for Ropley and the associated incoming selector would be connected and the three stored digits sent to the local selectors.
If the digit was 2 a junction hunter would seize a circuit to Alresford and the three stored digits pulsed out, the incoming selectors were on the second selector shelf there.
Calls to Alton went on direct junctions from level 3, again the incoming selectors were on the second selector shelf.
Part of the changeover from the PAX to the new exchange involved removing the incoming relay set at Ropley, a temporary arrangement took place where a code was needed for Alresford and Ropley calls while this work was undertaken.
from Turntable June 1st 1985
from Turntable January 14th 1984
Three photos taken by Eric Langley
Medstead PAX showing the rear of one cabinet and the external connection point, MDF is too grand a word for this.
Medstead new exchange - showing Rectifier 110, MDF and line tester
Standby batteries for the new exchange at Medstead - a modified signalling cabinet.
PABX3 final selector
One major problem with the Strowger system is that a call will connect to the first free piece of equipment, if for any reason this cannot handle the call successfully, for example a selector cannot mechanically step, the call will fail, the caller will try again and if the exchange is not busy there is a good chance they will get the same equipment again with similar results.
A modification that had been made at Alresford and Ropley had removed this problem. After a call a selector or junction relay set would busy itself out of service, when the last item in the group was used the others would be restored to service, safeguards were built into the system to prevent exchange isolation if for some reason only one piece of equipment remained free and it could not be taken into use.
Due the lack of space it was not possible to have these modifications at Medstead and often the exchange became isolated due to a faulty selector.
One alteration made was to fit a PABX3 ringer at the rear of the group selector cabinet to keep tones standard across the system.
Only known colour picture of the PAX at Medstead, shown is the rear of the final selector/line finder rack, the group selector rack is behind - a rather cramped exchange.
Alton
A redundant PABX3 from the MAFF in Winchester formed the basis of this exchange and completed the system. Numbers were in the range 34XX.
The 50 point line finders had fitted on a narrower rack than the standard 4'6" racks we were using, 8 position final selectors bank multiples equipped the rack but these were not used.
Two ringers were installed.
On opening it was connected by underground cable to Medstead, no overhead route was ever provided by the Mid-Hants.
The same selector shelf arrangement existed as at Alresford, again a maximum of 50 extensions. Levels 2 and 4 for Alresford and Ropley went via a common junction route to Ropley (UAX 0 and 1 relay sets) and level 5 for Medstead, calls to this exchange went on direct junctions and not via the tandem.
A PP223 was used initially before being replaced with a PP2040.
When recovered this exchange went to Project Red Sand, a WW2 anti-aircraft fort in the Thames Estuary.
from Turntable 2nd November 1985
from Turntable 7th December 1985
Rear view of relay set rack, selectors and line finders on back rack Teleprinter 15 on the left
Junction relays sets on the right also shown is the 4 channel carrier shelf
On extreme right is one of the soldered MDF blocks
Later view of same racks
Shelf C - local 1st selectors Shelf D - i/c and 2nd selectors Shelf E - final selectors
The small selector on shelf E was a patching selector, if an incoming selector became faulty it could be replaced by the patching one to maintain service, this was in the days of bothway junctions and it was not possible to back busy junctions.
Relay set rack
Krone distribution strips which replaced soldered blocks
Exchange recovery - 62 type carrier rack on the left
Alton exchange and signal box - the cabinets contained the standby batteries until replaced by a PP2040, old power unit shown awaiting collection for scrap.
Gas recombination cells replaced the lead acid type in the external cabinets
Medstead developments
The PAX remained in service until 1995 when it was replaced by a new exchange in the new S and T building, this was based on recovered buildings from a BT repeater station at Steeple Landford in Wiltshire. The old PAX equipment went to the Bluebell Railway for further use.
Picture shows exchange during installation
The new exchange was another hybrid, formed from 3 UAX13 racks, bank multiples from a UAX13, selectors from a PABX3 and UAX14 plus home build relay sets, 25 extensions were provided using line relays from a PABX7 and the 25 point linefinders from UAX CCB equipment. Numbers remained 51XX.
One mechanical ringer was provided and later a prototype electonic tone and ringer set was provided, although it worked very well only one was ever made.
The power unit originally installed proved very temperamental with little control over the output voltage, later replaced with a PP2040.
Junctions connected this exchange to Ropley (0 and 1 relay sets) for levels 2 and 4 and Alton via level 3.
This was the ideal size exchange, nice and compact, the other exchanges took up more space but one had to use what equipment was available at the time.
The equipment has been saved for further use on the the railway.
Electronic tone generator can be seen in the shelf top right, it is the second unit from the left. Electronic ringer is on the far wall.
Exchange maintenance
Original power unit, distribution fuses and MDF which was later replaced with a Box Connection and Krone strips. Line tester shown was a type used in TXE4s and modified for local use.
Exchange recovery - the ever helpful Sunday PW gang assisting
TRS huts at Steeple Langford Wiltshire
Site after wooden huts removed showing modern building
Home