Nice big Rivera 120 Watt amp came in today. Very heavy at 5.5 tons. Blown mains and HT fuses and 4 output valves (EL34) looking decidedly unhappy. Out with the chassis, 4 softish sacrificial EL34s fitted, quick check for obvious faults and a current limited power up. Initially seemed to work, output looked a bit odd. Negative grid bias wrong at about -10V instead of about -35V. This explained the look of the orig. valves. Grid bias was changing, but no way could you get it anywhere near what it should be. Then noticed something odd, in Standby (no HT on the valves), there was a sort of weird output. Then a miserable smell of capacitors electrolyte. I mention all this in case any amp repairers out there stumble across the same thing; Cut a very very long story short, various capdensors on the power supply board (left chassis in the picture) had leaked their gastric juices all over the place. Now, on this board, you have 500VDC, – 60V, +/-12 etc…. All these were tracking like made and eventually I ended up with a UV sun tan as the PCB carbonized and went up in an arc light and a puff. All components off the board (all unwired), cleaned and replaced as needed. Cut away burnt sections, re-varnish. Replace the board and now we had a nice -37V on the grids and the valves no longer running at 759 degrees centerfarad. Basically all DC conditions were mucked up by tracking on the board. Amazed it managed to work at all. Popped a fresh set of EL34s, now for the invoice.
