MATAMP GT120 Troubleshooting and How to Bias

I had a cool amp come through the shop with some strange noise issues. The first two preamp tubes were generating noises. I did a lot of troubleshooting to find out why the amp was eating tubes and the cause had nothing to do with the amp at all. It wasn't until the customer brought me another amplifier with the same issue. It was then I asked him detailed questions about his setup and found out they were running the incorrect high output send from a digital modeler into the input of the amps. The too-large signal was frying the input grids on the first stage preamp tube and them swapping tubes would just fry the next ones too.

I have that repair documented as well and will include a link and update this video with the new information when I can. I repair a lot of amps and tour around the world so it didn't dawn on me to revisit this video.

In the process of service I make sure to clean the sockets with Deoxit and check all the voltages throughout the amp and make sure there are no shorts or partial shorts when things get warmed up.
I get the amp biased up for the client and make sure it can handle being played on 10 before sending it out the door!