HELP!!!.....So here is an updated list of all the issues my Fender Bassman 1966 Blackface amp head has: 1) Subtle and sometimes louder crackling noise that goes on even with no guitar plugged in. Usually responds increases or decreases with volume knob. 2) Sometimes crackle and fuzz builds up then makes a pop and goes away, only to build up and pop and cut out again. 3) The Bass channel did this wierd thing where everything sounds detuned. 4) If you dig in and play with attack, the signal cuts off and then will come back on a few seconds later. Any experience with this? I'm assuming it could be the tubes, but any other ideas before I throw down the money and change them?