Testing non-electrolytic caps to find the "shielded" end

[Diablo]

It is not quite clear what you mean with noisy. Leaky or cracked caps can produce differend kinds of noise but they do not by themselves generate hum.

But like any conductive surface connected to a sensitive circuit point, a cap can act as an antenna to local hum fields. (Seems your body/hand was at least one of the hum sources.)

Hum intensity will depend on existing hum fields, cap size, cap position/orientation, closeness to grounded parts like pot casing or chassis.

I can't think of a way deterioration of a bright cap could increase hum sensitivity.

Does your amp have a "ground plane" like a metal mesh or foil that covers the chassis producing a closed Faraday cage?

No Faraday cage on the amp, just built like a Fender Tweed from the 1950s. I hadn’t played the amp in a few years, and it used to be a fairly quiet amp relative to hum. I recently installed a PPIMV Lar/Mar style in the amp, and that’s when I noticed that the bright channel had more hum than the normal channel. I started swapping tubes and tapping wires and components with chopsticks to see if I could isolate the problem.

[Diablo]

If not 'silver-mica disease', this is an interesting read anyway: https://www.antiqueradios.com/forums...ic.php?t=61153

Interesting, I’ll ask my doctor if can write me a prescription for cannabis to cure my chronic silver mica disease.

[Helmholtz]

No Faraday cage on the amp, just built like a Fender Tweed from the 1950s.

You might cover the inside of the back panel with aluminum foil to improve the shielding. Can be useful in a "noisy " environment.

[Diablo]

I’ll give that a whirl.

[catalin gramada]

It looks like as time any builder looking for neaty wiring, keeping wires as shortest or as close to ground mass or orthogonal posing, twisted or whatever...to claim to have not care about cap orientation looks more to deny any sense of you care about you wiring work, except maybe the proper neat wiring work was not done from aesthetically purpose. The term : "to avoid any.." should be use here. It is a very good practice to keep in a builder routine....as basic as measuring any new components before solder into a circuit.

[Chuck H]

I've only ever soldered one bad, new component into a circuit. An 80uf/500V electrolytic cap that was (probably) sold stale from Mouser. I have no way to "test" that appropriately before installation anyway. I've tested many other components before install, but not often known new components and I've never had an out of spec. or bad component. It just seems like A LOT of time to test every component going into a build or repair before installation. Mostly because it's an out of process step. When I'm stuffing a board (or "placing" the components ) it's pretty much:

grab, stuff, bend, repeat.

If that became:

grab, set meter for proper read, hold component without touching leads while still placing meter probes on component leads, confirm value, set meter aside, stuff, bend, repeat

stuffing a board could take a very long time.

I really think the odds are in your favor and the chances of a new part being bad are vanishingly small using new components. Though I know it has happened and so I wonder why it hasn't happened to me more.

[catalin gramada]

I.m even worst. I smoke two packs of cigarettes per day (not quite, but close) but don't recommend to anyone.


Just kidding...