Microzotl start-up filament flare?

I have recently purchased a Berning Microzotl which I am using as in my office as a headphone amp and to drive small monitors directly. I have noticed that the filaments in the 12AT7s glow very brightly for about .5 sec immediately after start-up and then settle back to a soft glow and stay that way. Is this normal? I will check with Berning next week, but was curious about it and wanted to know if anyone else has noticed this. TIA. And Happy Holidays.
The reason is that the resistance of the filament increases dramatically when it gets hot. So when you first turn on the amp, the filaments are cold and there is less resistance to current, so a larger amount of current flows through them until they get hot, so more current means more power, so this is dissipated as heat, so they are brighter for a second while they warm up.

It's normal, enjoy your amp.

How do you like the amp. I am using a 3 watt 2A3 amp with my duos but I'm curious about this amp.
Herman- Thanks for the info. I love this amp. So far I am using it primarily to drive HD-600 cans. It is very transparent, fast, smooth, plenty of detail, lots of extension at both ends. I am awaiting a pair of pretty nice monitors to try it out as w/speakers. Probably some of the transparency is the elimination of the need for a pre-amp and extra ICs, since I am using this in my office w/only one source (CD). In fact, I like it so much, I am now looking for a ZH-270, if anyone has one that needs a new home. If you are in the northeast, you are welcome to come for a listen.