Large capacitors lose their form over time and no use. I don't know how to explain this further. I'm an electrical engineer, but I'm tired and my brain isn't on yet I guess. If amps sit for an extended period the capacitors will degrade and when subjected to voltage later, they may and probably will fail. This is why it is always good to turn an amp on every few months if they are in storage. to charge the caps and have them keep their form. It is very easy to check. Have a technician use a variac and slowly bring the voltage up to nominal voltage and let it sit for awhile. A slow charge sometimes will allow the caps to re-form if they have been sitting for some time. After that, you are good to go. However, I would not recommend plugging it in and just turning the thing on if it has been sitting for a long period. Slow voltage increase with a variac is the way to go.
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