Identifying Mesa Boogie 6L6GT STR-440

[PhantomBox]

Hello everybody and a happy 2020.
I'm trying to identify MESA BOOGIE 6L6GT STR-440 power tubes.
I am about to buy a matched pair of new tubes from a private buyer who doesn't know a lot about this stuff. All he says is that the ones he is selling are replacement tubes for his Mesa Boogie triple rectifier.
Does anyone know if it is printed somewhere on the box or directly on each tube?
Thanks in advance.

 

[6A3sUMMER]

Carefull,

6L6, 6L6G(T), 6L6GA, and 6L6GB have max plate dissipation 19 Watts, max 360V;
and max screen dissipation of 2.5 Watt, max 270V.

The 6L6GC has max plate dissipation 30 Watts, max 500V; and max screen dissipation 5 Watt, max 450V

Some guitar amplifiers do abuse the output tubes.
And if they were designed for 6L6GC, then use 6L6GC.
Using 6L6GC tubes in an amplifier that was designed for the earlier versions of 6L6 will not hurt anything if you can adjust the bias currents.

Which do you think will last longer, 6L6GC, or the others?

 

[PhantomBox]

I'am buying these particular 6L6's for a friend of mine. He wants these tubes in the STR440 version, and I am doing him a favor, he actually is (just) a guitarist and really doesn't know anything about the technical aspects of a guitarists life...
That is where I come in...
Maybe you know a little bit about this misterios STR440 classification. What does it actually mean and what about other STR - types?

 

[PhantomBox]

Never mind.
Just found something on the web:
https://www.mesaboogie.com/media/Files/tube-guide.pdf
and
STR ratings for Mesa tubes? | TalkBass.com

 

[6A3sUMMER]

Look at:
Mesa 6L6 Tubes - GC STR-440 Duet | Humbucker Music

The side of the tube has a marking: 6L6GC
That is the only high power version of all the 6L6 tubes. Accept no substitutes. Needs to be GC.
It also has markings Mesa, and STR 440.

I do not have guitar amplifiers.
But I have built Hi Fi amplifiers using JJ 6L6GC tubes.

 

[PhantomBox]

Thanks, 6A3sUMMER.
I also found a similar image of these tubes on Amazon (I guess?)