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Old 12th Nov 2011, 3:31 am   #51
westcliff's Avatar
Join Date: Jan 2011
Location: Essex, UK
Posts: 349
Default Re: KB FB10 "Toaster"

Thanks for the information Rich. The output transformer hasn't been touched. It's one of the few components I've not had to work on.

Late tonight, after everyone was in bed, I put the set on the dining table and prepared to test the smoothing capacitor voltages. It was plugged into the lamp limiter, which was plugged into the RCD.

The first capacitor I tested was the one with three connections. I couldn't get the voltage at switch-on as I needed one of my hands for the switch, but I got a reading seconds later. It was at 214 volts DC and slowly went down to just over 206 volts by the time the set had warmed up.

Then I realised I couldn't hear anything. I optimistically tuned into Radio 4 on LW and it sounded just right. The set was switched to MW and the nearest station on the dial, a French one, sounded good too. The FB10 was picking up stations all over the place and there was no buzzing, humming, or crackling, just programmes.

I left the set running, tuned to Gold, while I washed the dishes and tidied the kitchen. Then I switched the lamp out of the circuit for full mains and it continued to work as it should. There was a feeling of warmth above the 6V6 output valve and the rest of the set was cool. The only smell was a faint "old radio" smell.

The smoothing capacitors are definitely okay. Would a bad solder joint at either end of these capacitors cause humming? I'm asking because the capacitors were not easy for me to fit, being axial. I didn't have any tag strips and the capacitors are "floating", with relatively long connections covered in heat-shrink tubing. Possibly not my finest work.

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