Thanks for replying Mr Fahey. It is a 'brown unit' and alas I bought it 2nd hand and it came with no schematic. Everything is on the one circuit board.

Hi there gents (and ladies). I've had this little amp (Acoustic G20-110 solid state) for about 25 yrs with no issues, it's been a great practice amp. Of late it has developed a problem. About 5-10 mins after I have turned it on, it loses volume rather dramatically, and the sound is all fuzzy and crackly. The sound is as good as ever until this happens. Any ideas please? Thanks in advance.