David, I would let it set on the peg in Cs off mode for a fewdays. It can take a long time for some tubes. An external HV supply can also be tried if it does not come down in a few days. If it does come down turn the switch to operate to turn the filaments on. The ion pump should peg again, that's OK it will slowly cycle up and down as the filaments de-gas. Eventually the pump will come down for good and the tube will warm up all the way. Then you can test and see if it has some life. Does your unit have the 10811 style oscillator? Is it a standard tube or a high performance? What is the part # like 1924-00156? I might have a good used tube available if it does turn out to be dead. Cheers, Corby