schematically speaking

There are numerous sites, such as these: (http://www.stereomanuals.com/) (http://www.audio-circuit.dk/Schematics.htm), that offer schematics and service manuals online. Yes- Caps can always be replaced with like values, but different sources. One power supply mod, of great sonic value, is replacing bridge rectifiers or standard diodes, with FREDs or Schottky diodes.

I assume you are new to electronics. See if you can find anything about discharging the power supply caps. A lot of amps will hold dangerous levels of voltage in their power supplies. Learn how to drain these (caps) first. Shutting an amp off while music is playing may drain some voltage, but even if it does, you need to discharge the rest of its voltage first.

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Tweaking a solid state amp would be much more difficult than a tube amp. Tube amps usually have more room to work in and are generally much simpler circuits. Solid state amps on circuit boards would be more difficult.

One great benefit is getting rid of electrolytic caps and replacing with oil/film or other film caps but the sizes required in a solid state amp would generally be so physically large that getting them in the chassis would be a problem.

Of course tube amps are a bit more dangerous with higher voltages.

Get some books on basic electronics. Prowl around over at Audio Asylum in the Tube DIY forum or other DIY sites. Google "DIY audio" for a lot of good sites. Maybe take a few classes at a local technical school or community college. There are a lot of sources with ideas for working on tube amps that are geared toward guitar amps but the principles are the same.

good luck