I bought a 500 mono off craigslist a few weeks ago. Seller said it played, but distorted. I tubed it up yesterday afternoon and I got nothing. I had all the needed caps on hand so I swapped in all but new can cap electrolytics and tried again. Nothing. I looked at it sitting there powered up and not playing and realized the three 12ax7s did not have heaters going. Checked the manual and the three have their own little heater tap off the power transformer. They are in series using pins 4 and 5. Checked the yellow and red wire that is supposed to feed these - got 0V measured against the chassis. So, I have a bad power transformer winding correct? In the event that I can't find a replacement transformer, can I get a little transformer to supply the heaters for those three 12AX7's and hide it below deck? If so, can anyone tell me how to choose a transformer? How does a winding go bad?