The Telephone on P.E.I. - TT Pad Modification
Member: Telephone Collector's International 2003/2004
For what it is worth, here is a little modification which was used back in my early Ham Radio days to add a touch tone dial to a DT-75 so that it could be used on an auto-patch on two meter repeaters. The modification used a Northern Telecom #NT35Q3A2X touch tone pad.
The original configuration of this pad in the phone is (in case you want to revert but check your phone's wiring against this first):
To use it as a TT pad for interfacing to a radio, it would be used as follows:
The L-Pad was adjusted for proper deviation on the DT-75. Battery power supplied by a 9 volt battery. The microphone ground was run to the intersection between the red lead and l-pad resistor. I have drawn this largely by memory - it has been a very long time since I have used this circuit, but thought someone would find it useful for something.