Peavey Classic 50/50 Valve guitar Amplifier.
Owner brought this little treasure in. Said the fan had become noisy so he disconnected it. After some time after, it started making strange noises through the speakers then went dead. Okay. Here we go.
No current being drawn from the mains power and fuse blown. So off with the bonnet. Not seen one of these before. Piggyback board with 8 x EL84s. 4 in parallel push pull in each channel. Strange being stereo for a guitar amp. Having a look around, 4 of the EL84s looked as is they had had a hard life with all signs of getter deposit missing. The others didn’t look too great either. The piggyback board is connected to the main board by ribbon cables, all ready to break after you have flopped it back and forth a couple of times during testing. Then noticed soot deposits on the underside of one of the cables and a burnt area on the board.
All 8 valves off to have a meeting with the AVO valve tester. 5 were found to have no emission, heater to cathode leaks and one with all kinds of internal shorts. The remaining 3 worked but were very tired. Cut away carbonized areas of the board and wondering what had happened. Was the amplifier used without a loudspeaker connected? With all that repaired and a fresh set of EL84s fitted, we powered it up with dim bulb limiter. 50% happiness was a reward. Channel one seemed to be working well. Full power and even clipping. But, channel two had a low distorted output with loads of hum, accompanied by a cherry red anode of one EL84 and no heater signs on another. Loads of dry joints, bad valve sockets and a couple of open resistors. Still could not understand why the output was low and had 50 Hz hum. Whilst all connections seemed to be okay using a meter, eventually found that one valve socket had a tiny trace of solder bridging the pin 2 grid and pin 3 heater supply. With that cleared we now had a working amplifier.
Very time consuming. It begs a question of how much do you charge for a repair? A set of 8 x EL84s will set you back the price of a 1947 Rolls Royce Silver Wraith, plus my obscenely high hourly rate. Then I think, well the owner did disconnect the fan. Anyway, I get to use 2 bits of test equipment that were made the same year as I was.
