I have recently obtained a whole bunch of tubes, and I now have a good collection of GE 6201 (always have the "GE etch" 6201 below the labels of various manufacturers). Anyway, I test them on my AVO Mark IV to make sure they don't have shorts and are reading close to spec, etc. After this, I would like to experiment by trying various 12AT7 types in the reverb driver of my '65 Princeton Reverb. Currently, I have a blackplate 12AT7 tube (Sylvania label, not sure what type in reality) in this position, and it sounds great. However, in the past I have experimented with various other tubes, and most of the time the reverb quickly lost depth. I have read that this could be caused by the tubes not responding well to the heat generated by the high current drawn by the reverb driver tube. I have also read on various tube dealer's web-sites and elsewhere that JAN GE 12AT7s do not last well in the reverb driver socket. What do you all think? I don't really want to "destroy" my GE 6201 tubes by experimenting with the reverb driver socket, since they could be useful elsewhere (phase inverter in other amps, etc.). I also have several RFT, Siemens, and other makes of 12AT7 types that might be better to try. Thanks!