I have built a small SE amp -12ax7 and 6l6- and it works although there is some distortion at high volume. The problem is it seems to have a ridiculously high voltage on the plate. The voltages shouldn't be that high , it's around 350 volts on the plate socket before I plug the valve in , but it goes off the scale ( 600 volts) of my meter when a valve is inserted..it has actually killed my meter ! I don't want to do the same to my next meter - is this a known effect of something , bad valve or opt? The meter was still reading normal screen voltages and preamp B+ voltages while this was happening before it died.