This was an interesting one, a Willsenton HiFi amp (made in China) brought in for fault diagnosis and some upgrades. The fault was a very intermittent pop in one speaker, this was traced to one of the four output valves and was left for the customer to sort out, but while I had it he wanted some mods done such as upgrading most of the power supply resistors to better quality ones with a tighter tolerance, the same with the resistors on the output valves, a few of the capacitors were replaced with audio grade alternatives, the heater wiring was replaced, as was the wiring from the mains input to the on / off switch and back to the power supply transformer, deleting the voltage selector in the process. Then it was on to the voltage regulator valve which was supplying a single feed to both preamps, this was split to provide individual feeds to left and right preamps, as well as all that the two filter caps were upgraded in voltage and a couple of resistors were added to the bias circuit to prevent meltdown in the event one of the bias pots went open circuit…and it could have gone on, there are a lot more upgrades suggested for it but we stopped there, when you consider the six capacitors in one of the pictures cost over £70, you can imagine this was not a cheap exercise. Anyway, it’s back at home now and hopefully sounding good.
