pls help!! temporary noise in my Pro Reverb

[Jazz-O-Sonor]

Hi,
Please I need some help with my fender Pro Reverb
project amp , below I described the malfunction;

Well , the first thing I do is to let the amp get warm using the standby, then I switch the power on and the amp reacts very strange with a lot of nasty intermittent
noise (similar to interferences) , the sound appears and disappears when I touch or hit very lightly the cab of the amp , but after almost 10 minutes everything become normal , the amp sounds normal without noises at any volume and dosen't even
react with noise anymore when lightly hitted .
Any idea of what could be the cause of this ?

thank you , John

[RWood]

I would chopstick the plate load resistors and B+ dropping resistors during warmup when it is making the noises to see if you can ID the culprit(s). Then replace with metal oxide resistors of appropriate wattage. Old resistors that have absorbed moisture can make those sounds when current is running through them, then through use they dry out enough to quiet down. Chances are good they have drifted in value, too, so they should be replaced.

You don't mention how new or old you amp is, but if you post a schematic we can tell you which resistors I'm referring to.

RWood