I swapped all the tubes one day with some Sylvania EL-34's I acquired with another amp as well as the rectifier tube. I don't remember if I checked the bias like I should have (was inpatient to try the tubes) after running it at moderate volume levels for about an hour one channel cut out.
I shut it down right away. And found the Cap board had got hot. The wrap on several caps swelled and 2 resistors that are tied to pin 8 of the rectifier tube look burnt. I am thinking the rectifier tube shorted??
Here's my dilemma.... looking through this board it seems the SDS cap board may be problematic. I think I remember reading other posts on fried SDS boards. I am debating on re-populating the board or putting a upgraded quad cap and bias circuit. I was pretty happy with the way the amp sounded but not sure about rebuilding the cap board every few years?
Also, if it was a shorted rectifier tube that caused this. Would the rectifier modification (adding 2 1n4007 diodes in series with the rectifier tube) possibly prevented the fried cap board?
Any advice or thoughts would be greatly appreciated.