Power Tube Difference

[hunter1970]

Ok I'm new to tube amps, recently acquired a Peavey 6505+,and my question is what do all of the different suffixes stand for,my amp uses 6L6GC
What does the GC stand for and what's the GC STR, GCMSTR represent.
And how does all this relate to my 6505+.

[Twitch]

"GC" means glass case as far as I know, as opposed to metal case, but you dont find metal case except NOS military tubes. As far as the "STR", I havent a clue other than Mesa likes to put that as a part number for their various tube options.

Nowadays, the suffixes really dont mean much. For the most part, forget anything but the tube designation. If you amp takes 6L6's, then 99% of anything marked 6L6/5881 is compatible, doesnt matter if its GC, STR, R etc. If its preceded by 6L6 or 5881, youll be fine.

[plon]

"GC" means glass case as far as I know, as opposed to metal case, but you dont find metal case except NOS military tubes. As far as the "STR", I havent a clue other than Mesa likes to put that as a part number for their various tube options.

"STR" is Special Tube Request. These tube designs were requested by amp makers. I read this on a few other forums when I was trying out tubes for my Mesa.

[Cygnus X1]

"GC" means glass case as far as I know, as opposed to metal case, but you dont find metal case except NOS military tubes.

Close, but not quite.
For 6L6 you might see older "GB", then a little later "GC", with B and C being slightly different.
The "G" does stand for glass envelope.
Oddly on 6V6 you might see old 6V6G...coke bottle style large glas, then "GT", smaller glass envelope.
And the "GTA", a later standard.

Metal case was standard when these tubes were introduced, not mil-spec.
I have metal 6V6, 6SC7, 6SN7's, and glass of each as well.

5881 isn't always safe for a 6L6GC designed amp, the plate voltage might be too high for it.
Same with a 6V6G, can't always replace 6V6GT.

[Twitch]

Wont argue with the amp guru I was told that now a days, 6L6 and 5881 dont really differ like they did years ago. Id go with Cygs explanation here hunter.

[DonP]

"GC" stands for Guitar Center

I kid....

[Cygnus X1]

Wont argue with the amp guru I was told that now a days, 6L6 and 5881 dont really differ like they did years ago. Id go with Cygs explanation here hunter.

You're right about that part, the difference was removed.
The 5881 was upgraded to be able to take the same voltage specs.
Older 5881's are great, but not a direct swap for an amp designed for 6L6GC's.

"Guitar Denter"...

[Twitch]

Well the tube conspiracy theorists down at The Lone Gunman tell me that its even deeper than that. Ive been told theyre all 6L6's now with different part numbers to make it appear your buying a different tube, when in reality your getting the same tube rebranded as a 5881. :dunno:

So are the older 5881's close to the bias required for EL34's? Not that low??

Also Cyg, if 6L6's are actually beam tetrodes and not true pentodes like the EL34, how do they make some amps compatible with both beside the switchable bias range? Ive noticed that 6L6's only have 6 pins, where as the EL34 has all 8. Obviously all parts of the pentode must not be in use when used in an amp designed primarily around the 6L6? Are the EL34's actually running as triodes in these amps?

[Cygnus X1]

Also Cyg, if 6L6's are actually beam tetrodes and not true pentodes like the EL34, how do they make some amps compatible with both beside the switchable bias range? Ive noticed that 6L6's only have 6 pins, where as the EL34 has all 8. Obviously all parts of the pentode must not be in use when used in an amp designed primarily around the 6L6? Are the EL34's actually running as triodes in these amps?

Fugg if I know!



Something about the EL34 having unused pins and internal jumpers.
That's the kind of thing I have to look up.

[hunter1970]

So GCMSTR doesn't stand for Guitar Center's Made Special Tube Request.

[Cygnus X1]

So GCMSTR doesn't stand for Guitar Center's Made Special Tube Request.

Sorry I, we tracked way off to another discussion.
"GC" is standard designation, meaning glass envelope, "C" is latest revision in design as of maybe 1965, just guessing the year.

Anything after that such as "STR" is purely subjective, and may mean "Special Design Request".
Bottom line is if they are working fine, don't get so trigger happy to replace them.
People tweak power tubes far more often than they should....IMO.

And if you do replace them, suggestion is Winged C, really any good matching set of 6L6GC's will work.
Tone is the key to which ones you are happy with.
I know it's expensive but I always recommend to carry a full set of matched (by bias) tubes if you are gigging it.

And get it biased!
Get it biased!
Get it...biased...just in case you don't already know.
Don't ever blindly swap out the power tubes without biasing.

You can change preamp tubes at will, no biasing needed.

[Chief_CrazyTalk]

All I know is I use EL34s or 6CA7s.

[Twitch]

And get it biased!
Get it biased!
Get it...biased...just in case you don't already know.
.

Yeah, it seems Cyg and I feel we cant stress this point enough (read my ENGL post).