So I have two Marshall Valvestate amps... one is a valvestate 8080 112 combo, and one is a valvestate 8100 head. They both started having problems at roughly the same time, the combo would occasionally howl and feedback, and the head was having volume drops and swells, and I figured replacing the preamp tubes would probably fix the problem. When I opened them up, I realized they are pretty much the same amp internally, the only real difference is one is 80 watts and the other 100. They had different kinds of tubes, but when I bought new tubes I just put the same kind in both amps. Now we get to the problem. Both amps now have VERY low volume on the gain channel. The clean channel works normally, but the gain channel is just not there. Anybody have any ideas? This is the first time I have ever replaced tubes before, but it kinda seemed hard to mess up... Thanks in advance.