R1155 progress

Restoration of the R1155L is not progressing well at the moment, digging into some of the more inaccessible areas has uncovered a number of burnt resistors and wiring around the bias board. Most of the burnt bits appear to be part of a modification done by a previous owner, who in future I'm going to refer to as Bill the Bodger (a British term for a person who makes or repairs something badly or clumsily). His shoddy efforts have really created a lot of additional work for me.

It looks like Bill has attempted to re-wire the Meter Amplitude potentiometer into the bias circuit, although without a lot of effort I'm not going to find out why. I'm guessing that it might have been intended for variable RF Gain, but whatever it is it will have to come out.

On a more encouraging note, I was delighted to find that the two VI103 'magic eye' indicators I bought last month are both usable. The R1155 uses one as a tuning indicator, driven by the AGC voltage. Unfortunately the phosphor that gives the green glow seems to fail very quickly, resulting in a very dim display even though the valve emission is still good. Finding serviceable originals is now very difficult; New Old Stock (NOS) near-equivalents are available, but these are getting expensive.

VI103 'Magic Eye' on test, control grid grounded.

The seller said they tested OK on his AVO valve tester, but he didn't give any indication of how bright they were. They probably aren't as bright as they should be, but they are usable and at the price I paid I'm definitely well pleased with them. The seller was in Eastern Europe, so it might have been interesting to find out how two British Air Ministry valves got there.

From Eastern Europe via eBay!

The original VI103 in my set had been replaced with an EM34, a similar civilian indicator with a slightly different 'eye' shape. Fortunately I have now discovered that the pin out of the two types are slightly different, so the wiring of the socket must be changed back before I re-install a VI103!