Re: Roberts RT7 - problem
An Alkaline PP3 battery will last a long time, not much point in paralleling as the discharge from each may be a little different and become unbalanced.
The other possible cause is the driver transistor being damaged, though as you have had some sound this seems to be working. A damaged output transformer is one possible cause of the output transistors failing, as the new ones are still overheating from what you have described, this would be harder to replace unless old spares can be found.
I personally would only change the larger value electrolytics at the moment, it is unlikely that the small value non electrolytics would cause this type of fault unless one has gone short circuit in, say, an input to the driver stage and this doesn't happen very often. But if you are ordering it might be more economical to get everything in one go, depends how much you want to spend on it.
Geof
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