12AX7 Flashing

[dumbassbob]

I bought 3 different Philips Mini Watt 12ax7s from 3 different places when I put them in a cheap good bad tube tester they All have a glow orange Flash on the input filiment just for a second..They still read "Good" but none of my other 12ax7 tubes do this ,and I have 30 different RCA,GE, SYLVANIA,Mullards.Only the Mini Watts have this flash on the one filiment

[kleuck]

Phillips, Mullard, and Matsushita 12AX7 exhibits this flash, wich is perfectly normal.
Thats in relation with the filament coating.

[Jazz P Bass]

If it is "Heater Flash" I would expect it to be o/k.

[riz]

Yep, seen it on an old Mullard. Unnerving if you're not expecting it, eh?

[kleuck]

Indeed