Spax 12AX vs. 12ax7, how to see the difference?

[andershoeg]

Hello.
I have messed a little too much with my mesa preamp tubes that came stock with my f-30.
So, I was wondering if it is possible to see any physical difference between the input tube (spax 12ax7) and the other tubes?
B.r. Andershoeg

 

[zodiac272]

Spax7's should be no different. They are 12ax7's from the same bunch of tubes that happen to be less microphonic and nothing else. Sonically they should be the same. they are all 12ax7... just the Spax7 are branded different cause they test better

scott

 

[MrMarkIII]

The SPAX7 has a black rubber jacket around the glass.

 

[andershoeg]

Thanks for your answers.
I don't see any rubber anywhere.
I was trying to figure out if i had put the right tube in v1. But unfortunately i can't really find out 'cause there is no real difference that i can see. Well, sounds good anyway
B.r. Andershoeg