I've seen this happen on more than one occasion, typically with a 60s or 70s Fender amp where the first pair of mains caps was incorrectly installed. I assume someone who didn't know what they were doing got a hold of the wrong schematic and went to town. or someone didn't double check their work. Either installed in series incorrectly or in parallel incorrectly, that is either the wrong polarity or with both caps wired in parallel as follows: Red - Neg cap lead (opposite lead tied to other cap). Black - Neg cap lead Red - Pos cap lead (opposite lead tied to other cap). Black - Pos cap lead What amazes me is that these amps seem to still for a while but sound like ****. and then Strange things noises etc start happening within the amp. Can anyone say what would the likely failure modes and symptoms be? Along with componants to replace? It is obvious, the mains filters, yes but I'm wondering what other electrical stresses this causes. Thanks.