Hi there,
I've been through three Bassman 500 amps within a couple of months , all with the same problem.
Was looking at getting something to give me that Svt grit with half the weight. Tried the heads with multiple cabs and still pop.
Sent the first one back to fender same thing. They claimed first off that the wrong type of fuse was installed, then when it happened again they said it could be the voltage in the area, as they are based on 230 volts rather than 240 and that could be behind it. After the third head I just wanted my money back. Really disappointed, when it worked it sounded great. Was hoping the problem would go away.
I think that there is a whole batch issue that fender have on that particular consignment or the design cannot cope with 240 volts and has a bad design in that area. Real shame....