Complete newbie to amp repair

[Cliff Fiscal]

recently acquired a '79 Vibro Champ. I love small tube amps, and this one has great tone---at love volumes. Anything above, say 4, and total breakup on the bass notes. Not good tube breakup--broken speaker type fuzzy crap!

I plugged a 2x12 cab (8 ohm, I know is bad for a 3.2 ohm amp, but it was only plugged in for about 30 seconds).

Same nasty breakup above 4 on the bass notes. Muddy crap.

I know this amp is capable of great clean Fender heaven.

I was going to take it to a local amp tech who was going to charge me around $120 to replace the caps, and generally tune it up.

Then it occurred to me---Why don't I learn to service tube amps myself, being that I play them and all. Might be a useful thing to learn.

Here are my questions:

1) What is causing the bass notes to mush up like that?

2) How hard is it to service tube amps for someone with no knowledge of such things? I have very crude soldering skills.

3) How hard is it to learn to work on them, what is the best resource for said learning and how long does it take to become semi-proficient.