tube question
 

i have a GT12ax7 in my amp- then a friend gave a me one, its looks the same but has 'premium' stamped on the tube, i cant seem to find a reference to this thing, i gotta feeling its the same exact tube but made at different times

I'd really need to dig out my copy of Aspen Pittman's book, but there's two possibilities. It's either a better build of tube, such as a JJ vs Sovtek or similar, or it's a tube that passed a screening process for gain and microphonics to weed out less desirable tubes. Are there any other markings, and could you possibly post a pic or two of them for comparison's sake?

Haven't used Groove Tubes in years, but there are very definite tonal differences between different 12AX7 tube types depending on internal construction, date of manufacture, country of origin, etc. - all of which a savvy player can use to custom-tailor his/her tone. The last published catalog shows no less than a half-dozen 12AX7 tube types, each with its own characteristics, and while none of them are designated "Premium" they do show a more expensive version with matched triodes (highly recommended as a driver/PI tube IME, or in all your preamp stages if you're looking for a smoother/tighter, more-even/more-controllable tone); here's a copy of their 2012 catalog for reference:

http://wpc.077D.edgecastcdn.net/0007...List_Final.pdf

I agree that a matched triode tube is desirable for the phase inverter in most push-pull amps, but that is assuming that everything else in the phase inverter is well matched. In some amps, a trimmer is installed in one leg of the PI to accommodate for those variations - or intentionally balancing the PI for sound rather than what it says on a meter.

For other stages in the preamp, matching the triodes is even less important, because all stages are in series (with exceptions such as some Matchless amp with parallel triodes in the first stage), and the variation between triodes in a 12AX7 is negligible.

Bottom line: Matched triodes in a 12AX7 are not so necessary in a guitar preamp - more useful in a tube preamp for audiophile applications that are designed and built to tighter tolerances. Matched OUTPUT tubes - yes, please.

looking closely, i guess they are different- but i cant find any info between the 2 types

it probably depends upon who manufactured them for groove tubes. are there any other numbers on the tubes? otherwise it MAY be a marketing tool.
you can test each one in, i'm guessing, v1 and see if there is any difference in sound. just because one is premium doesn't mean you will like it better.

play music!

Truth be told, I never really understood the need for triode matching until a knowledgeable electronics tech (by trade)/audiophile (by hobby - guy designs/builds his own equipment) suggested it, after he had opened up/checked out the innards of my amp on his bench...

Works for me, does everything he said it would - as with anything else, YMMV...

They do look different in bottom section, Maybe you could contact Grove Tubes and get some info

Tubes
 

There may be some difference between premium and the regular. I doubt if anyone can "hear" the difference. The tubes my be spot tested and one batch may have better specs than another.

In the audio range any 12ax7 will perform as well as any other. As they age and approach the end of their life you will hear a difference.

Some years ago I went all solid state and got rid of my tube amps.

I have serviced industrial electronics for 39 years some tube equipment early on. So I have a good working knowledge of electronics.

One of the amps was a old Fender Deluxe. I removed the tube chassis and replaced it with a Fender Sidekick 65 I cut down the chassis to fit in place of the old one. The result was from a distance it looked like a old deluxe.

I used it in a pit band for a variety show. After the show one night a "tube person" came up to me and said "nothing beats the sound of those old tube amps". I said no they don't. He couldn't hear that it was not tube but solid state neither could I or anyone else. So the observation in this case is if it looks like a tube amp then it sounds like a tube amp.

I now use a Loudbox Mini. The Sidekick got rebuilt again into a small light bass amp.
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well, it was a pain to change them by and forth- tell you the truth, if there was any difference, i couldnt tell

I can say that the GT 12AX7-C is a rebranded Shuguang 12AX7-A. My guess is that the premium vs non is just a Retail vs OEM or a Matched vs Non-Matched tube.