Another January 1999 topic, I thought this may be of some use even though the P4 Mk.1 TOU is no longer available since similar designs can be readily made up from curtain track and PC board. The original text and illustration follows click on the illustration for a larger version.
Point operation by Post Office relays.
The use of GPO Relays in conjunction with P4 TOUs (Originally published in "Prototype" issue 17, November 1977)
My club in Australia managed to purchase a complete telephone exchange of obsolete pattern when it was replaced with a larger one. It cost us $10 to hire a truck and two week-ends labour removing it from site. Amongst other things this yielded over 5000 relays and a vast number of 80 pin plugs and sockets, not to mention enough cable and wire to wire up a telephone exchange! Bearing in mind that H & M and similar point motors cost $4.50 in Australia means had to be found to use these relays instead.
Various methods have been devised by members for use on HO layouts and proprietary tracks. For P4 use the scheme described has proved reliable over 2 years use. Basically a triangular extension piece is bent up from P4 rail, soldered to the armature and a slot cut in the end with a razor saw, the tab provided with the P4 T.O.U. is crimped in to the slot. A bracket is required to hold the relay to the baseboard and in my case these were easily sawn out from the chassis of the telephone exchange. If the contact springs of the relay are not required for electrical switching they can be bent to increase the strength of the return stroke, otherwise an additional spring could be used, in most cases, however, a relay with multiple contacts has enough spring strength.
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Copyright Keith Norgrove.
Last revised: March 21, 2008