[A.N. Beal]

Dear John,
Sorry to be slow to reply. I don't have any test equipment apart from a multi meter, a mains tester screwdriver and pair of old speakers to connect to the amplifier when poking about with the plastic chopstick. However having identified a dry joint on a tape connection socket I resoldered the joint - and since then the amplifier has run perfectly, with no crackles, no funny noises and no odd changes in volume. It appears that the tape socket joint must have been the problem - strange. However at least it is fixed. Thanks for your help.
Regards,
Alasdair