st-70 tube flash help

When I turned on my amp last night I noticed that the 12au7 tube flashed in the lowere area of the tube for a second or two. It did not seem to affect anything but decided it would be best to turn it off until I got some information from the "knowledgeable one's". The driver board is a Triode Electronics. The 12au7 is set between two ef86's.

What is the significance of the flash? Can it damage the amp? I will await to hear some feedback before I proceed.


If the tube is an "Amperex" (Bugle Boy)on the label or the date codes, then it is normal.
Many European tubes flash on turn on. Its notmal, and its not just Amperex. My EI's flash - some do, some don't, but its normal. Use your amp.
If its the filament itself that glows brighter the first second or two.Make sure it is the filament only.The exact same spot should go back to its normal glow.Those tubes that do this kind of flash will always do this at turn on from a several hour could start.If your not sure,by another tube and check it out to be safe,plus you'll have a spare.

Thanks for the reassurance and facts on the tube flashing.
I've been a member just under a year and really
have learned a trmendous amount by just reading the postings.

I am hooked on the site and continue to improve my system and more importantly my appreciation of the music I listen too.

Thanks again, Lawrence