Technics SA GX130D receiver amp keeps cutting out

Question

Hi. Had this receiver amp for about 13 years which has always been very reliable. We moved house in the summer and the whole stereo system was in storage for about 3 months. I set it up again last week and now the amp cuts out after about 5 minutes. If you switch on and off it starts again and each time you get a little longer out of it, going up to about 40 mins.
Wondered if you know what the problem might be? Thanks guys.