I have an '87 Marshall JCM 800 2210 100W half-stack, and at unpredictable times it just cuts out completely, then cuts right back in a few seconds later. This can happen regularly for a few minutes or not at all on some days, it's extremely frustrating and very unpredictable.
The head doesn't seem to be affected at all and so I would assume that it would be a fault with the lead connecting the head to the cab or possibly something wrong with the cab.
If anybody has had a similar problem or has a clue about how to fix it, any help would be much appreciated.