Are new tubes supposed to do this?

I have a pair of VTL Mono 120 that uses 4 807 tubes per side. Previously it had Chinese Shinto tube that came with it but I decided to change to a few of RCA and General electric tubes that I had on hand.

After changing and making sure I had the correct bias, I pressed play on my cdp but about 5 min. into the song, all of a sudden there was a very bright flash almost like a burst of lighting discharge came on in of of the tube accompanied by a very loud static noise from the speaker. I got scared then hurried to turn off the cdp BUT not the amp to make sure the music stop. The flash went away. When I remeasured the bias point of that specific tube again, it read almost 0V (260mv is the recommend bias point). I decided to try playing the cdp again to see if the same thing would happend again but this time, everything seemed fine -- no flash nor pop -- and the music didn't seem to suffer in term of quality.

But to make sure that the tube itself was not to blame for the bizarre thing, I then exchanged for another Ge tube. I then turn on the amp again but right at the moment when the amp was turned on, there goes that big flash again in that same tube position which prompted me to turn of the amp immediately. I told myself what the heck, held my breath and turn on the unit one more time. BUT this time there was nothing, just a small static sound but went away immediately after 1 or 2 second. I then replay the same song for about 10 minutes but everything sounded fine. I then turned off everything, waited another 15 min. to turn the amp on again, everything seems fine now but initially there is still a few soft tick and pop but then it all went away.

One thing I did which I thought might have caused it is that I change the tube when the amp was still warm. I don't know if you have to wait for the amp to cool down before changing the tube.

I am new to tube but I don't know if anyone had similar experience or know what was going on with what my amp? I will probably try to call VTL on Monday to see if they know anything.

By the way, RCA and GE tubes sound a lot more transparent, airy, more 3D, bigger soundstage than the Chinese tube. I just couldn't believe the differences.