Attempting to discover why an old Luxman tube-preamplifier didn't sound too good, I drug out the Hickok Cardmatic tube-tester this morning.
I noticed that 6 of the 7 12AX7s tested off-scale (to the right, above 100). New 12AX7s that I tested ran from 80 to 90 on the scale. Is there a problem with an off-scale reading? There was no indication of leakage or gas in any of the tubes. Also, all of the tubes that tested off-scale had another characteristic: Upon powering them up in the tester, the wires in the base that evidently connect to the cathode lit up bright red to almost white for a short period of time, perhaps a second or two. The new tubes that I tested did not exhibit that characteristic. Any thoughts on this subject? 73, Barrie, W7ALW
