It's alive!
It sounds great. No hum. Very little crackle from the pots, except as predicted a little from the 'balance' pot. I very happy and not a little surprised.
I found the 100W bulb in the spare room ceiling lamp in the end! Am I safe to remove it now or should I run for a while with it in place? Once I remove the bulb from the circuit am I likely to see any issues?
Thanks for all the help, so far!