It took me a week or so to find the time to check out the amp and my observations were not exactly conclusive - I still had an intermittent problem, but had it just become more intermittent?
Receiving no reply by 20 February, I re-sent the email with the comment "Hoping this will appear on your radar this time..." (see below right).
This was the first indication that the initial quick response from Bruce might not be typical. However a response did come - see part 6.
Thanks for your prompt reply, sorry it's taken me this long to acknowledge it. I played around with the box connections and hooked it up in line with the red side of the reverb tank rather than the black side as it had been, and the one time I have been able to use it since, I have not noticed it cut out completely, and the signal level into the reverb appears not to be causing symptoms of overload.
I would be interested to know the details of the sensitivity mod you mention. If it's just down to cutting the wires on one capacitor, I think I could handle it.
I had another good look for a serial number on every surface that is visible without removing the chassis, without success. Was it just a self-adhesive sticker that could have been peeled off?
Thanks and regards,
Hoping this will appear on your radar this time...