Ok, Folks who repair these old/reissue Fender tube amps..
Here are a few beneficial tips, if not known, or considered, from someone who has repaired/electronically restored hundred`s of them since 1975.
If the amp has a tube driven reverb circuit, do yourself, and the customer a favor during the sine wave/or playing testing of the tremolo/reverb channel, if the reverb tank drive output transformer is not connected to the tank`s input, or a 8 ohm 2 watt dummy load, or even a 8 ohm speaker(though the sine wave sound, can be annoying after a while), the reverb transformer can fail, via the primary winding opening from no reflected load on the class A configured 12AT7`s paralleled triode sections..
I found this out decades ago, and constructed/soldered a RCA plug to a standard 3/4" spaced dual banana plug with a 2 watt 5% 8 ohm resistor that I soldered across it, to protect the driver transformer, and to connect the input of my test equipment`s dual banana shielded cable to check the reverb circuit output..
Another, sometimes, oversight, is to make sure all jacks, and controls are secured tight, as they are part of the grounding. and also make sure the front panel`s control/jack brass ground buss is well soldered to the chassis(a large wattage/soldering tip iron is needed)
And as a matter of course, IMHO/E, all the small tube 100k plate carbon resistors should be replaced, as they will usually become noisy/start making popping/crackling sounds soon enough, if not already starting to happen..
Just some thoughts folks