GT10 problems

[zintere]

I bought a 1976 Ampeg GT10 from a guy who said it worked last time he used it. I plugged it in and it seemed to be working fine. I turned the volume up to about half and it quit . All I get now is a slight hum and some crackling sounds. No smoke , no smell just hum and crackle. I replaced all the electrolytic caps , still nothing but slight hum and crackle. I also tried a different speaker and got the same results. The hum and crackle do not increase if I turn up the volume. I would appreciate any help.