Tube amplifier bad caps

You have probably NOT ruined the tubes because of this, unless one of the conditions below occurs. If your tubes are driven into oscillation over an extended period, then I would worry. Also, if your tube bias circuit goes bad somewhere and the tubes glow red-hot for an extended period, I would worry then, too. I am not sure if this is comprehensive, perhaps someone else may add to this. As far as my experience and my father's advice to me on a problem with my amp goes, this about covers it. He is a retired EE professor by the way.
Are your tubes glowing red-hot, or noticeably brighter than usual? If so, and you let them run this way for a while, get them tested. Otherwise, see how they sound after you have fixed the crackling problem. They should be fine.
Good luck with your amp!

Just a quick observation that bad caps don't necessarily have a visible external leak. I've seen plenty of way out-of-spec ones that appear physically fine.

Do you have a voltage meter? Do you have a schematic that indicates voltages at various test points? (Keep in mind that voltages in a tube amp are often in the 400 to 500 volt range, or even more.) The key is to start a logical testing process to run down the problem.

Cleaning switches is a good idea (and won't hurt anything) but there are a number of possible causes for the noise. A bad solder joint, a resistor damaged from overheating, a mechanical foil trace failure, a smaller signal cap - any of these or others could be the culprit.

Man, this one sure sounds like a bad power switch to me! It **does not** sound like bad filter caps! It *could* be a bad tube, but the flicker really suggests that the contacts on the power switch are arcing and permanently damaged. I would fire the tech that gave you the bad filter cap assessment, and get the power switch replaced.

Atmasphere I like your style ..no BS

I would pay attention to Ralph's (atmasphere) comments.