So I sacrificed the Matamp to the Tone Gods yesterday. They were pleased so they rewarded me with a Model T. Its a 2nd gen and its spotless (pic in the post your rig thread). Its got a set of JJ KT 88 in it but the guy also included the original Tung Sol 6550 that came with the amp. I keep reading how these are a great clean pedal platform but this amp is anything but. When running the both input its dirty clean all day long no matter where I set the pre volumes. Still sounds great no doubt, but I haven't had a lot of time to spend with it and wonder if I'm doing something different than most people. It has gold pin JJ12ax7 in v1 and 2 and a Sovtek 12ax7wc in v3. I've got a 12au7 here at the house and a 12ay and 12at7 at the practice space. Should I pop those in there?
Speaking of tubes, can you guys help me with these questions...

This marking is on the back of a JJ 12ax7 but I can't find anything about it online.

I know this is an old Ei but is it normal for the tube to flash really bright when the amp is first turned on in standby or does it mean that the tube is going bad? I had it in my Soldano and it would do that so I took it out. It still sounded great, but i got paranoid. Its the only tube I've had that i can think of that would do that.