Audio Repair Tools

noromance has a good example of a global/generic toolset.

With George's suggestion, I'm always recommend against using vacuum to clean circuits and vacuum causes static electricity which could potentially damage some IC circuits (i.e. op amps, etc.).

George recommended a PCB spray cleaner.  I actually use different products and tools you can get from Digikey (www.digikey.com).  I use a can of Flux-Off (digikey part # ES835B-ND) along with Kimtech tissues (digikey part # 473-1118-ND).

Just lay down a tissue on the circuit board.  Then spray the Flux-Off on top of the tissue and use the brush that comes with Flux-Off to scrub the tissue against the circuit board.  This helps get into all the nooks and crannies.  Gunk and flux and other stuff will be scrubbed off and soaked into the tissue.  The Flux-Off dries quickly and without any remaining residue.  This leaves a completely clean board.  You might want to order a couple cans of Flux-Off.

You can look into small pliers and tweezers if you need them (probably not for disassembling an amp).  There's a cheap Aven Tools tweezer/pick set from Digikey (digikey part # 243-1178-ND ).

When searching for these on the digikey website, just put the part number into the search box.

With George’s suggestion, I’m always recommend against using vacuum to clean circuits and vacuum causes static electricity which could potentially damage some IC circuits (i.e. op amps, etc.).

You use a brush and it sucks air, there’s no static, you don’t put the vacuum nozzle on the components. All techs I know tv or hifi do it this way.
And here's a link that works for the PCB board cleaner 
https://www.jaycar.com.au/electronic-circuit-board-cleaner-spray-can/p/NA1008

Cheers George

Thanks for all the suggestions. I should have been more specific. The filth is not so much on the circuit boards but mainly behind and in the hard-to-get-to corners of the amp casing. I can see it with a flashlight but I can only barely touch it with an elongated Q tip. I suspect this poor amp was stored in the basement for years because the owner didn't want to deal with fixing the left channel circuit board issue. If you press down on the circuit board, the left channel pops into place. Let go and the channel goes out. Otherwise the amplifier sounds nice in spite of the filth and even oxidation on some of the circuit board components. This amp even had an old dust encrusted spider web complete with dead spider. Disgusting!!!