Hiwatt Hi Gain 50

Problem: excessive hum from speaker.
Solution :
Often caused by faulty capacitors not smoothing the rectified ac properly however in this amps case it was something else as well.  In this amp a number of op amps that are used for the effects send and return loop are powered by  a 30v supply.  It’s worth checking this as in ones case it had significant ripple caused by a number of minor components. Unusual because the current draw from the op amps would be minimal.