Small tube instantly light up brightly during power up

[xiawei]

It then dims to barely noticeable level. The sound is fine to me. Is this normal?

[Natural Sound]

Some of the British tubes do that and it's normal. Do your voltages look OK?

[xiawei]

Yes, it passed all test. I'm new to tubes and so far, my tubes on the wa6 amp don't do this.

[Natural Sound]

I can understand your concern if you've never seen that before. I've seen Mullard, Ei and Valvo tubes do this. There may be others that behave like this as well. If the voltages are correct, it doesn't stay bright and the sound is good then don't worry about it. Here is a short video (not mine) of the tube flash that I believe you are experiencing. Again, this is perfectly normal. Enjoy!

[williaty]

I just rolled some Amperex Made-In-Holland Bugle Boy 12AU7s that I was given into some of my Bottlehead stuff. Given what the tubes are worth, it scared the crap out of me when I saw that tube flash for the first time. I was very relieved to find out it was normal when I searched online.

[Grainger49]

When you turn on the amp the tube heater is cold.  This is the lowest resistance it has.  So the inrush current is the highest, the glow the highest. 

In a second or two the heater is warm and the current drops appreciably.

[xiawei]

When you turn on the amp the tube heater is cold.  This is the lowest resistance it has.  So the inrush current is the highest, the glow the highest. 

In a second or two the heater is warm and the current drops appreciably.

Then why the other big one is doing this?

[Paul Birkeland]

It then dims to barely noticeable level. The sound is fine to me. Is this normal?

This is often referred to as the "Mullard Flash".  We probably sent you a particularly nice 12AU7 with your kit.

6080's just don't do this, the behavior seems specific to 9 pin Mullard tubes.