Hi All, I'm new to the forum and have found it extremely valuable when building new gear! Thank you for that! Looking for some guidance/recommendations: I've completed my JTM45 build coupled with a dual greenbacks cab and am completely flummoxed at this point. I've been playing the amp at lower volumes consistently throughout the past 2-3 months since it has been built and the amp was singing! I felt confident enough to gig it. While trying to push it at performance levels with my accompanying pedals, the main fuse blew. This occurred when I was running a Zvex Mastotron which draws ~1mA. So naturally I replaced the main fuse 3A and tried again. Amp was singing beautifully (15 minutes at performance levels) until I ran the masty again. It sounded perfectly fine for ~3-4 minutes then the mains blew again. My measurements are fairly accurate to the metroamp layout so I'm not sure what the next step is. At this point, I bought another set of matched KT66's but am hesitant to replace the fuse and try again for fear of further damage to PT. HT fuse is in tact, fixed bias is around 45-48mA; there is some oxidation happening on power tube pins but nothing is out of the ordinary, and just to reiterate when the amp was on it sounded wonderful with no strange hisses, buzzes, cracks, pops, etc... Hoping to find some recommendations from the group if anyone has found themselves in a similar situation. I can send anymore information... otherwise, to the amp repair shop I go. Thanks in advance for any replies!