An amp Q not asked in awhile....

[Dave Hopping]

My 2014 Twin-Reverb (now in a head-cab) sounds fine until it gets warmed up, then starts in with an intermittent 60-cycle hum, along with a few pops and crackles. A soft-to-fairly-firm-heel-of-the-hand tap on the top of the cab stops the hum for a few minutes, then it starts up again. I'm sure it'll need to be looked at but it'd be nice to get some thoughts from the SGF amp guys about the problem. Thanks in advance!

[Colin Boutilier]

My first step would be cleaning the tube sockets and pins.

[Dave Sneed]

Could also be a cold solder joint…. As the amp warms up the joint expands breaking whatever electrical path it’s supposed to be completing.

[Dave Grafe]

Twin Reverb (and Dual Showman) amps tend to run pretty hot and tubes do die, especially in working environments. The noise occurs when well warm, is affected by shock, and persists afterwards, gave you replaced any tubes with known good ones?. The next time that noise happens give each individual tube a light flick with your fingernail and see if anything unusual happens. A slight "tink tink" sound is normal on preamp tubes, but any change in noise, volume, tone or clarity is your clue. Passing this test does not mean they are good, but it's the easiest way to spot a possible problem without tube swapping.

[Raybob Bowman]

Sounds like symptoms of bad filter caps. Usually amps older than 20 years need filter cap replacements. This amp isn't that old but there was a thing called "capacitor plague" as Wikipedia speaks of in 2007 where bad electrolyte was used in cheap caps that were failing in many things. It's possible Fender was using older stock of cheap filter caps. I know in 2010 it caused failure and my brand new refrigerator and new TV back then.

[Dave Meis]

With the power off, remove the phase inverter tube (closest to the power tubes). That isolates the pre amp from the power amp side. Now you're just hearing the power amp side. Turn it on, take it off stand by, and let it warm up. If you hear the noise, it's *likely* the power tubes. If not, it's in the pre amp section. If it's the power amp side, definitely try cleaning the pin/sockets as suggested above.
I just went through this with 2 of my amps in the last 2 weeks... hiss, intermittent white noise, whistling, humming after it warmed up. Changing the power tubes solved both amps. My Twin runs around 500 vdc on the plates, and the Tung Sol STR tubes are the ones that hold up for me, but I hope it's something cheaper.. like a preamp tube!