• 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.

VTA ST120 - Troubleshooting - Only 1 Channel Operational

Hi All.

I'm seeking assistance in solving a problem with a tubes4hifi ST120 that I built about 4 months ago. The unit only plays through 1 channel. It's a long story as to how this happened, though in summary, I managed to insert and seat one of the the KT88 incorrectly. It was rotated by 1 pin. When the unit was energized, the 100k resister popped, there was smoke and a fair degree of cursing. I replaced the resistor, thinking this was the only part I damaged, though the unit still only plays on 1 channel.

I've performed many comparative tests, though cannot pinpoint what other parts need replacing.

My first question to the forum is: Has anyone performed something similar and can help me pinpoint the problem?

If not, I'll add to this post in the coming days as to what I've done to try and identify/ isolate the broken part(s).

Regards.
Andrew