A Power Supply for the T1154/R1155 (/cont)

220V Supply & Audio Amplifier

Don’t use semiconductors …

The audio output from the R1155 is designed for high-Z headphones. The noise in a Lancaster bomber (Halifax or Stirling) was unbelievable! The operator had to wear headphones, a loudspeaker would have been totally impractical. However, here is a really simple beam-tetrode design to accommodate a loudspeaker. I used a Russian 6P1P which has characteristics similar to a 6V6 or 6AQ5.

Note that in the PSU, the -ve side of the 220V is NOT connected to the chassis. This is because in the R1155, the chassis actually ‘floats’ to allow a -ve bias of about 30V to be produced. The 39R resistor is chosen to match the characteristic of the valve rectifier, in this case an EZ81. I didn’t have a suitable smoothing choke, and if I did, I doubt I would have had room for it, so I simply put a 300R resistor between the two 33uF capacitors. Quite by chance, the on-load voltage is 217V which is precisely the output of the dynamotor. S3 and the 3K3 resistor serve to provide a ‘Standby’ facility. A jack socket is provided for high-Z headphones. This is actually necessary when operating the T1154 in CW or MCW mode since the side-tone is fed to the R1155 audio stage and is too loud for me via the loudspeaker!