Again, I'm wondering how a rectifier can fail - it's under-spec'd for the job, an AC power surge during a bad electrical storm, power supply capacitor does not have a DC path to ground to discharge when the amp is turned off thus discharges thru the rectifier diode (bad design) or failure due to age i.e. fatigue due to repeated on/off cycles - for this amp has to be really old.Shorted power rectifiers are a common problem in many amps. There is nothing surprising about this, nothing to do with any of the issues you mentioned (although they can be influences). Sometimes they just fail for no reason.
My 50W, 8ohm amp can't drive my 86db, 4ohm speakers? WTF??
OK, I am only writing this tongue in cheek. Recently my integrated amp stopped working so while I wait for it to get repaired I just tried to use my 10 year old Sonos ZP-100, rated at 50W, 8ohms to drive my Sonus Faber Guarneri Evolutions speakers. I knew the results would not be stellar but I just love listening to music everyday I was hoping the Sonos would get me by for a few weeks. Sonus Faber speakers are notorious for being power hungry and my Evolutions did not disappoint in this regard. These speakers are rated at 25-200W, 86db, 4ohm. At low volume the sound is alright but even at moderate levels, around 70-75db I start to hear what sounds like a slight buzzing/distortion at the upper mid range. Its not really obvious unless you are familiar with the song. In looking at the review Stereophile did of my speakers, the impedance does indeed drop to 4 ohm at 200hz and 4000hz so what I am hearing makes sense. I assume this is my Sonos clipping? If so, I am surprised that it would clip at such low volumes. I thought clipping occurs at higher volumes? I knew the Sonos wouldnt be able to really drive my speakers but I did not expect it to sound so bad at such a low volume. Oh well...I will keep counting the days until I get my amp back.