• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Help - how to tackle unknown problem that sounds near fatal!

Hi, sorry to sound dramatic, but I have been tending to an old ARC SP8 with your very generous help and been really close to completion with only a residual hum left to finish. Oh and it was sounding lovely today and then......

An oscillating volume/ a pop and loud buzzz. I muted the amp and then turned it off. It has done something similar in the past when I decided to get it repaired, and it came back with errr... hum and hiss. It also did the same a few weeks back when I plugged in a friend's CD player, I had just assumed it was some crazy inept cable + socket management on my part and ignored it.

I have not turned it on again, and wanted some advice before I do.

Is there a protocol to minimise the potential damage of what seems such a dramatic problem by turning it on to investigate?

Earlier today in my search for hum I checked all the obvious voltages and it was apparently spot on (or very near)

Thoughts?

😕