Preamp tube flashes at turn on?

[KeithC]

I have an NOS Brimar 12AX7 that flashes right when the amp is turned on.
It does it in every position except the PA.
Anything to worry about or is it just a characteristic of the tube?

It works and sounds fine otherwise.
Other tubes in the same positions don't do it.
I thought it might just be V1 on the amp but I moved the Brimar and it still flashes.
This is a JTM45 clone BTW.

Thanks....:AOK

[Dave C]

Flashing at power up seems to be common with European tubes , I don't know why.....maybe someone else will chime in.
Dave C

[rockon1]

Like Dave C said. I consider it normal.:)

[teleamp]

I've got a sweet old Bugle boy 12AX7 that flashes at turn on, it has hundereds of hours on it since I got it with no problems.

[Old Tele man]

...it's the same phenomenon as with incandescent light bulbs!

...at turn-on, filament resistance is "low", so LOT's of current is immediately drawn until the filament heats up and its resistance climbs into the "normal" operating range.

...and, "yes," it's during "turn-on" that most filament failures occur due to the sudden inrush of current

[brad347]

OTM: Why don't american tubes do this?

Every mullard and amperex 9-pin tube i've ever had has done this.

[Old Tele man]

...because they (USA tubes) incorporated "time-delay" (typically about 10-11 seconds) filament "turn-on"...that's the "A" suffix on 6V6GTA, etc.

[KeithC]

Thanks for all the info. As always good advice and lots of knowledge abounds around here!

[GenoBluzGtr]

all my mullards do it... none of the USA tubes I use does it. That's a very interesting fact, Old Tele Man... thanks