Another R1155A resurrected … (/cont)

This is the finished article; fully working and laced up. I wish I could say that it worked first time, but it didn’t. For various reasons, work had been interrupted once or twice and as a result, a couple of minor wiring errors had crept in. Then during some initial HT voltage measurements it was noted that the bias on the Mixer-Oscillator was incorrect. This was the valve that had been replaced with a 6K8G. I removed it and fitted an ex-equipment VR99 and the discrepancy was resolved. Alignment was more or less straight-forward. However there were a couple of issues relating to the DF circuitry. The Meter Amplitude control worked in reverse and the Meter balance control was unable to null out the imbalance. The latter was identified as a valve issue by swapping V1 and V2. In doing so the imbalance flipped over the other way. I chose V1 and replaced it with an new VR99A; The Meter Balance control was then able to null  

out the imbalance. The problem with the Meter Amplitude control operating in reverse was a curious one since the wiring appeared to be fine. However there were two types of potentiometer that could be fitted. I replaced the ‘standard’ pot with one with a 6K5 resistor on a small tag as per my AD8882B. This fixed the problem. So I think there might be a problem with the way I interpreted Peter Holtham’s wiring diagram for standard 3-terminal pots. Murphy’s Law struck soon after lacing up the wiring. The set failed on Range 3. Or rather the Local Oscillator became slow to start on that range. This turned out to be an issue with the VR99 that I had fitted. Replacing it only temporarily resolved the problem because I then noticed that L4 in the first stage was no longer tuning. This did not bode well because to remove L4, I was going to have to de-solder connections under the coil-box. The R1155 was never designed to be maintained! In 1943, the life expectancy of a bomber was only 3 weeks! I managed to extract L4 and found that the iron slug had become detached from the Bakelite adjustment screw. I replaced the entire L4 assembly with one from my box of spares. I could have been forgiven for thinking that that would be the end of my problems. But no! The set then stopped working on range 1, then it finally failed on all 5 ranges. This turned out to be a Local Oscillator injection issue and was actually caused by failure of the VR99 mixer-oscillator … again! So I replace it with a NOS VR99 and it has worked fine ever since. The thing you have to remember with the R1155 is that it was never

Intended as a high-spec communications receiver. The presence of the BFO served only to render CW signals readable. There are also more controls on the front panel related to Df’ing than to actual reception. As a general receiver of AM broadcast stations it performs very well and this one even compared rather favourably with my RA1772 at 17.5MHz. I think it is worth the effort restoring these classic receivers just to get a feel for what it was like for the young men who operated them and the companion T1154 transmitter during WW2 and as a testimony to them.