Rebuilding a classic Ampeg SVT bass amp

[Ohioan]

In 1984, at the age of 17, I bought an Ampeg SVT from someone. I used it up until around 1991, and then set it aside. Over the last ten years it has been sitting in a barn, unfortunately. Today I retrieved it and removed the chassis. Here is a link to an album of photos I took today:

https://www.flickr.com/photos/194366...77720323179456

As can be seen, the chassis is a little rough, and there is remnants of a mouse nest.

The 6550 tubes were purchased in 1991, and have zero hours on them. Meaning... after I installed them, I never powered the amp.

My goal is to get this thing back to as close to 100% as practical. I am not in a hurry to do it, and I don't want to cut corners. And while I have next to no experience with guitar amp diagnostics & repair, I am well acquainted with electronics and testing. (I'm an EE and have been doing electronics-related stuff, both professionally and as a hobby, for 45 years.)

I have an ESR meter and decent DMM, and plan to measure the parameters of each component. For leakage current on some of the caps, I can borrow a high voltage power supply from work.

Am looking for advice, suggestions, etc.


Thanks,

Michael
Saint Paris, Ohio

[The Dude]

Too bad a mouse decided to make it home. The first thing I'd do is give it a good cleaning. Mouse pee is corrosive. The quicker you clean it up, the better!

[glebert]

I personally never bother measuring component values until I know if something isn't working right. For most amps (after cleaning) I will power them up slowly on a variac and light bulb limiter. The longer then amp has been sitting the slower I power it up. I will use small light bulbs at first, when I know it can get to 100% wall voltage with one size bulb I go up to the next size and slowly power it up again. For big amps I pull the power tubes at first. If I can get to 100% voltage with a big bulb (shouldn't glow much with no power tubes), I will repeat with power tubes, usually adding one pair at a time, but that may not work if your SVT has the tube protection circuitry.

If when powering up you see the light bulb flickering, hear popping sounds, etc, then back down a bit on voltage and see if it stabilizes, maybe even go back to a smaller wattage bulb.The goal with bringing it up slowly is to not slam the electrolytic capacitors with a huge voltage and current spike, and there is a notion that if the capacitors have dried out and gotten weak that limiting the current through them (that is the variac and light bulbs job) the capacitor can "reform" and perhaps be usable instead of blowing out completely. I recently did a Hiwatt DR103 that had been sitting for 25 years with the above procedure and it powered up just fine (though no mice on that one).