Not all models of the T1154 were capable of producing Amplitude Modulation (R/T on the Master Switch). The A and E models did not have this facility. In the airborne installation, the crew Intercom amplifier type A1134 was normally connected to the Microphone Input (+&-) on the front of the T1154. To cater for this, the link inside the transmitter had to be set for a ‘dynamic’ microphone as opposed to ‘carbon’ (see below). I tried a vintage carbon microphone and found the level of modulation to be pitiful. In fairness to the transmitter, this may well have been due to the carbon granules clumping together over time and thus reducing the output from the microphone. If I was going to use the transmitter in the manner that it would normally be used, an external microphone amplifier should really be used. A1134s can be found, but they are very rare. The amplifier was powered from a 120V HT battery and a 2V battery. Although the valves can still be found, there are two complex multi-winding audio transforms inside, and if one of these went faulty there would be little chance of repairing it unless you were very

lucky. I could have easily made a suitable pre-amp that would have fitted in a match-box. But I hit on the idea of a more fitting design using valves. It would need to be self-contained with it’s own PSU.

Self-contained microphone pre-amplifier

microphone pre-amplifier schematic

A Microphone Pre-amplifier for the T1154

mic selector plate