Something nice in to repair. QUAD 2 power amplifiers and a QUAD 44 control unit. Not a SMD in sight, no silly TDA… Class D chips to blow to bits, just good wholesome grown-up engineering.
Long standing customer brings in lots of HiFi gear, all quality stuff. The report was that one channel was dead. With only one interconnecting lead supplied, I wondered if that was the cause. No.
Starting with the Quad 44, this indeed had one channel missing. The signal on both channels could be traced all the way back to the rear sockets. One of the attenuating resistors had a crack and was open circuit. Very odd. With that replaced, we had both outputs. The balance control and Mono Stereo switch were a bit scratchy, so they were cleaned up. Other than that all was good.
Turning to the Quad 2s. Both amplifiers seemed to be quite original, valves and all. The first one had quite an early serial number. Snipped out the coupling capacitors and these were found to be slightly electrically leaky so were replaced with good quality types. Several high value resistors had become way out of tolerance, so these were replaced as well. With the amp powered up, the output was very good and produced full power. No nasty surprises and we had the lovely smell of hot dusty valves as they warmed up. The other Quad was a little different. Same attention paid to the capacitors and resistors as required. However, on test, the output was very low and very one sided. I hoped that we didn’t have a duff KT66. That would have been sad. After all, they had done 60 plus years’ service and would be nice if they gave a bit more. Both KT66s were running the same temperature, nice and hot, so obviously conducting. Then I noticed the EF86 inverter was cold and had no heater glow. Checking it, indeed showed the heater was open circuit. These valves are now becoming stupidly expensive to buy new. Luckily, I still have a reasonable NOS stash. Popping in a genuine Mullard to keep everything tidy did the trick. Both amplifiers were nicely balanced.
The client does tend to get a bit confused when connecting things up and seeing he had only one umbilical cable, I made up 2 phono cables hard wired to the Quad 2s, making it simple to connect to the Quad 44 control unit. All linked up, sounded very nice. I will look forward to servicing the setup again in 60 years’ time. I wish.
