I just had a problem with my ST-120 that needs your immediate advice before I go any further with troubleshooting.
I was listening to it when I noticed that the rear left side KT-88 (Gold Lion) next to the Weber copper cap rectifier was glowing very brightly. I thought I had burned a tube or was about to burn a tube. The amp was still playing away when I went to the amp and I could also smell something burning. I shut down the amp right away and let it cool off.
I removed the tube that was overheating and replaced it with another Gold Lion KT-88 I had that had very low hours on it.
When I fired up the amp again all the tubes seemed to be glowing normally and I tried to set the bias on the output tubes and there was no reading on my meter or should I say it read.002 milliamps no matter what I did with the pot adjuster.
This was the same on all 4 KT-88's at that point I thought it might be the rectifier and sure enough it was.
When I removed the Weber copper cap as it was discolored and smelled bad. I eased the top off it and the insides were completely fried and the two large ceramic resistors were both cracked and one literally fell apart. It was burnt to a crisp inside. Most of the diodes etc. were also showing signs of major overheating.
My question is not only what happened if you can guess but should I put a tube rectifier in there to see if it was only the rectifier or should I check something else first?
I live in Costa Rica and it is a long way to get another Weber. I have three tube rectifiers but I do not want to fry them if there is another common problem.
I'm hoping it is not a major problem with the amp and just a faulty rectifier. I haven't heard of a copper cap going like that but anything is possible.
I have built a couple of DIY projects and am capable of doing some diagnostics but I need to know what to check and where the problem might be.
Looking for a little advice here from the guy who knows this thing inside out before I sacrifice any more parts.