Steve I appreciate your thoughts on this problem I've got.
This PA amp has a four channel input amp, mixer amp , EQ amp , power amp and spring reverb.
My first attempt at a fix was to clean all pots and and inputs. Wiggling cables doesn't affect the the static [ pops & crackles ]
The static starts just as the amp warms up and then is at a constant rate.
The overall sound produced is clean and undistorted even at uncomfortably high volume.
The amp is in the same box as one 16ohm speaker, there is another separate box with a speaker. When I connect the 2nd speaker the static is at the same rate and level.
Basically it boils down to a constant level of static [ pops & crackles ] with either all pots at zero or at max. That is to say the static is constant with any of the component amp being adjusted for increase or decrease in master volume, seprarte channel volume, EQ or reverb level.