I have a 1964 Ampeg SB-12 that hasn't been used in decades. So I took it to Dennis Kager at Central Jersey Repair and had him go over the amp. Besides changing the plug to a 3-prong, the report came back with the amp in very clean shape and with a suggestion of putting in a set on NOS tubes (old ones were only putting out 20wts). I asked about the capacitors and he said they were fine. I forgot to ask what causes them to fail so does anybody know? I was suprised it didn't need them replaced.