Mullard 12AT7WA / CV4024 flash!

[Thoburn]

I received my Mullard tubes today and carefully installed them. When I turned on the amp I practically had a heart attack! The tube flashed bright white, and I mean BRIGHT white, before settling into a normal looking orange glow. It only lasted for a fraction of a second. I hope that flash does not damage it. It sounds fine so far (I'm only listening to FM).

[JC]

As I've mentioned before, this is not uncommon for certain vintages of European small tubes.  It had something to do with the formulation they used for "controlled heater warm-up".

It should behave the same way every time it is turned on from a cold start.

[Thoburn]

Thanks and yes, I have read that before, but I was shocked by the 'flash  bulb' intensity of it.

[JC]

It is shocking the first few times you see it!  Imagine firing up a vintage Marshall guitar amp with 3 or 4 of those little flash-bulbs in it---that was how I first was introduced to this!  I was dead-certain that a fire was about to erupt!