You might try a pickup & electronic cleaner on the,
input connections.
I carry a pick-up & electronic cleaner with me when i,
go out on the road.
Its made by (Electro-sound) i just had to spray into,
the inputs of one of my fender amps the other day.
It was humming plus cuting out and in.
Ask your music store about it its a life saver.
Most of this is caused by dirty contacts,from dust ect.
Also on one of my fender amps the silver box down,
in the bottom of the amp that controls reverb ect had,
dirty contacts also which i had know reverb untill i,
sprayed into the inputs in it.

hope this helps Mark