B-52 AT100 very low volume/fuse blows when standby turned off

[godwang]

Hey there fellas, new guy here. Really enjoying browsing around the forums, very informative!

My AT-100 has been collecting dust for about three years and has only been used a minimal amount of times since. It was working fine until I let my roommate use it for practice. If I change the fuse out in the rear and turn standby off, the fuse immediately blows and the volume of all the channels become barely audible.

So I opened it up and did some snooping:



The big blocky hunk on the left is what we're looking at on the previous photo.



After doing some reading, it seems that the power supply is susceptible to failure, and I'm guessing that's what it is (til somebody slaps me on the wrist and says "NO!" )

I have a lot of experience in soldering and wiring but very little experience in schematics, terminology, and potential dangers. Is this something I can be walked through and do myself or should I leave it to an expert?

Thank you in advance. Cheers!

[Jerry]

Does that amp have a tube rectifier and a SS rectifier and a switch to choose which one you'd like to use? If it's set for tube, change it to SS and see if your amp works that way.

[godwang]

SS is where it's been switched to the two times I've tried replacing fuses. I haven't turned it on via the two tube toggles.

[godwang]

Any takers?

[Mark Black]

Have you tried powering up & taking off standby with all the power tubes removed? (This to rule out a bad tube).

Additionally, to protect what is left that is good, do a forum search on "light bulb limiter". You will find all kinds of discussion on how to build one & why you should use it (instead of blowing fuse after fuse during troubleshooting).

The B+ fuse on the AT-100 protects only the output transformer/power-tube part of the circuit (along with a few related components), so that narrows things down quite a bit.