I have an issue with my vintage 1974 DR103, when I turn on the mains switch, sometimes, not always, it turns on and immediately off.
If I turn off and on the switch a couple of times, it works.
- Is it bad Mains switch?
- Does it need recap (the amp is still in its very original condition).
- Is it bad contact in tube sockets?
- Nothing of the above?

Thanks in advance!