Originally Posted by
Simon Barden
For short periods, it's not going to do any harm. Just don't leave it in standby for too long. Once it's on, you are better off simply turning the volume down than putting it in standby. After an hour or so in standby, you can get 'cathode poisoning' which will shorten your valve life considerably.
This is all new stuff to me too, and it's hard to unlearn the perceived wisdom of 35 odd years of playing through valve amps.
If your pickups have metal covers, then shielding the pup cavities probably won't give much benefit, but doing the control cavity will do. If you've got open coils, then shielding the cavities will help a bit.
There's only so much you can do to reduce buzzing if it's a really noisy electrical environment. After a certain level, it's going to break through regardless.