Tube designation ???????'s

[6stringdrug]

I am considering a tube change in my fender SCXD. My questions are many. What do the letters at the end of the number mean? Can a GC go where a S came out of. Can a 12au7 or 12 at7 replace a 12ax7? I know to keep the same number but am I gonna blow up my amp if I use the wrong letters? Is there a percivable difference in tone? Also, any suggestions for brand? I play mainly blues and classic rock stuff, some experimental. I am upgrading the speaker too, an eminence ragin cajun. I am so over my head here.

[tunghaichuan***]

I am considering a tube change in my fender SCXD. My questions are many. What do the letters at the end of the number mean? Can a GC go where a S came out of. Can a 12au7 or 12 at7 replace a 12ax7? I know to keep the same number but am I gonna blow up my amp if I use the wrong letters? Is there a percivable difference in tone? Also, any suggestions for brand? I play mainly blues and classic rock stuff, some experimental. I am upgrading the speaker too, an eminence ragin cajun. I am so over my head here.

Suffixes mean various different things.

NOS/vintage 12AX7 and 12AX7A: The "A" denotes "controlled hum and noise characteristics and is used in high-fidelity audio-amplifier applications" according to my RC-21 RCA Recieving Tube Manual. The "12" at the beginning of the number means the tube runs on 12.6 volts (or 6.3v if the filament is wired in parallel with itself). The "AX" is the specific type of tube. The "7" means that there are 7 elements in the tube: two cathodes, two control grids, two anodes, and one filament. There are actually two amplifying devices in the 12AX7, two triodes.

There are a few tubes that use the same pinout as the 12AX7: 12AU7, 12AV7, 12AT7, 12AY7 5751, etc., but they all have different characteristics. Generally you won't hurt anything if you use a tube with the same pinout, but different characteristics. However, a 12AU7 is not a low gain 12AX7, neither is a 12AT7 a lower gain 12AX7. However, the 5751 and 12AY7 are lower gain versions.

The other tube type used in your amplifier is the 6V6GT. The first version of this tube was the 6V6 and was in a metal casing with pin 1 connected to the casing. The next version was the 6V6G which was a coke bottle shaped glass envelope. The next version was the 6V6GT (GT stands for "glass tubular"). After that came the 6V6GTA. This tube got a rating increase from 12W to 14W, and the "A" in this case stands for controlled warm up. There also was a 7408 which was designed to be a high-fidelity tube used in hi-fi equipment.

All of the aforementioned was in the good old days of Western tube manufacturing. Now that most tubes are made in Russia, Slovakia and China all of that has gone out the window.

The JJ 6V6S is actually a 16w-19W tube, kind of a cross between a 6L6/6L6G and a 6V6GTA. I believe the "S" stands for Slovakia, where it is made.

I've got various Russian 12AX7 type tubes with WA, WB, WXT for suffixes. They don't really mean anything according to the old standards. Now most of the suffixes are marketing hype and are tacked on by relablers.

So basically, if you stick the the tube types you have in there, 6V6 and 12AX7, you won't hurt anything.

[sumitomo]

Robert oh Robert,Now Robert he can show ya how to change a tube! Sumi

[kiteman]

Robert oh Robert,Now Robert he can show ya how to change a tube! Sumi

Robert is our tube expert, can't go wrong with this guy.

[ZMAN]

I am considering a tube change in my fender SCXD. My questions are many. What do the letters at the end of the number mean? Can a GC go where a S came out of. Can a 12au7 or 12 at7 replace a 12ax7? I know to keep the same number but am I gonna blow up my amp if I use the wrong letters? Is there a percivable difference in tone? Also, any suggestions for brand? I play mainly blues and classic rock stuff, some experimental. I am upgrading the speaker too, an eminence ragin cajun. I am so over my head here.

I recently bought a used SCXD. I asked the same question over at the Gear Page. I also asked what would be a good replacement for the 12AX7, including all the letters.
I got 3 replies Sovtek 12ax7LPS, Tung Sol Reissue 12ax7.1.
I also got a reply that the 12ax7 was only being used as a phase inverter and any good quality 12ax7 would do. That poster recommended a
JJECC803S Hi Perfromance 12ax7 gold pin as an excellent phase inverter.
The price range locally was from 13.95 to 19.99, and I can pick them up locally (Canada) with no shipping.
Mine is a little microphonic, I still have the stock speaker though.
Neither the tube or the speaker is a big deal to change, and I am on par with Robert when it comes to changing tubes.