Hello All. I am working on a Marshall 1977 JMP MK II 100 watt. It was brought to me by a friend who said it was running hot and melted the plastic grill above the tubes! It was definitely running hot. Red plating the power tubes (6550s). He told me he had it worked on by another tech years ago, and it was never quite the same. I pulled out the chassis and found that previous changed the bias resistor to 100K. I thought restoring it to the proper value of 47K would solve the problem. Now it sounds quite good but it's still red plating even with the bias set as cold as possible. I am still measuring bias current. I see 393V (V4-5) & 394V (V6-7) on plates. Thoughts? Thanks in advance!