Gentlemen, If you look at the mfg. of the tubes that light up like that you will probably find that they are Telefunken or Amperex (Holland). While not all tubes labeled such will have that characteristic that does indicate they were made in the same facility regardles of label. I don't remember the exact reason for the momentary incandescence but believe it has to do with the construction of the filament from that Mfg. It's actually a good sign since that type are regarded highly by the audio world. As for the offscale readings... check the tester calibration as "new" tubes readings will depend on the mfg. and year made. I have quite a few new Phillips/ECG late production 12AX7's that do not test close to what a NOS RCA or GE, or even some of the used Mullards do. My Cardamatic, the WE ,KS series version of the Hikock 123A tests 12AX7's with a different card than ECC83's in that the bias is slightly different. Actually the parameters of the 5751 and ECC83 are the same. All tubes tend to loose high frequency tone with age. Kind of a softening of the high frq. response. But will still test good in a standard tester that uses line frq.as a signal source. The exception is the Weston testers which use an internal osc. at 5 khz which gives a more realistic test of the sound of the tube. Beware of most of the Sov. 12AX7's as they tend to be very thin sounding with their small plate structure. IMHO the long plate Euro mfg. or NOS US long plate styles have the best overall tone. Excuse the long reply. Hope it helps. Bill KB3DKS
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