Just got a used DB 728 delivered to me yesterday. Nice looking amp. Anyway I took it home, hooked it up, let it warm up and instantly after I hit the standby switch firecrackers started going off and then lots of smoke. Popped the lid off the bottom and my acute visual skills identify two 220 uF caps directly under the small (heater filament?) transformer are nicely cooked. So any idea what may have caused this? Could this be a sign of a major problem or is it possibly an easy fix? The tubes were all lit and glowing evenly. No other signs of malfunction besides the obvious ones I already mentioned. Any information and/or advice is greatly appreciated.