Do Preamp Tubes in Guitar Amps Need to be a Matching Set?

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Do Preamp Tubes in Guitar Amps Need to be a Matching Set?

Post by acjetnut » Mon Jun 30, 2008 7:49 pm

It's time to swap the tubes in my Fender Hot Rod. It uses 2 12AX7's as the preamp, and a third as a phase inverter. Do the preamp tubes need to be a matched set?

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Post by Scodiddly » Mon Jun 30, 2008 7:56 pm

No. The output tubes should be matched because they're working as a team, like two people rowing a boat together. The preamp tubes are in their own sections, and don't interact as much.

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Post by ZacharieDaquiriDoc » Wed Jul 02, 2008 12:49 am

How does one, voice an amp?
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Post by ImaginaryCat » Sat Jul 05, 2008 12:39 pm

Matching tube preamps is only a matter in a hi-fi stereo situation, if you want both sides as close as possible. And even then, just matching brand and era should be good enough.

To my knowlege matching tubes was something that Grove Tube thought up in the 1980's because they were selling Chinese tubes with very little consistancy. Previously to that people just put two tubes in and played it. Meaning all the legendary amps and legendary tones that everyone is after were made with unmatched tubes.

I actually purposely put unlike preamp tubes in my amps to make the two channels a little distinct. In my B-15 I have a NOS Soviet Military Spec 60's tube in one channel and the USA made Ampeg branded tube in the other channel, probably original. Both sound great, just a little different. If you've got a gutiar amp you can even try a 12AY or AT 7 in place of one of the preamp tubes. Sometimes I swap the phase splitter down to an AT, it's cool. Preamp tubes are plug in and go, swap them around, have fun.
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Post by paully » Sat Jul 05, 2008 4:42 pm

ImaginaryCat wrote:Previously to that people just put two tubes in and played it. Meaning all the legendary amps and legendary tones that everyone is after were made with unmatched tubes.
>>>>>>>>>>>>>>>>
LOL! You nailed it right on the head. Assuming the tubes are actually matched by the manufacturer or a retailer(as best they can be matched), after a few hours of punishment you can bet they're not matched any more. Plus the whole theory assumes that everything from the phase inverter forward is like 1%(or better) components; including the primary windings on the output transformer. The last time I saw close tolerances in a guitar amp was, well, NEVER :wink: .

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Post by Randy » Sat Jul 05, 2008 5:18 pm

ZacharieDaquiriDoc wrote:How does one, voice an amp?
What do you mean by that?

If you are wondering what in the amp you can change to affect the sound, it all depends on what you want. Almost everything in the amp affects how it sounds, the circuit, the speakers and cabinet style. For instance, suppose you have an amp and it's too "boomy." If it has a closed-back cabinet, you could try an open back to see if that tightens up the bass. If it is an open-back combo and it still has too much bass, you could change some capacitor values in the tone stack or on the preamp cathodes. You could simply find speakers that have less bass response. Or even more simply, you could try a different guitar and/or a different amp.
not to worry, just keep tracking....

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Post by rwc » Sat Jul 05, 2008 5:29 pm

it is important to match stuff that works together. like transistors in a class A/B amp. try using ones with different beta values, play music at a regular level, and watch what happens to the amp 45 seconds later...

preamp tubes, not at all.
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Re: Do Preamp Tubes in Guitar Amps Need to be a Matching Set

Post by Huntlabs » Sat Jul 05, 2008 6:37 pm

acjetnut wrote:It's time to swap the tubes in my Fender Hot Rod. It uses 2 12AX7's as the preamp, and a third as a phase inverter. Do the preamp tubes need to be a matched set?
Why do you feel it is "time". Tubes basically work or they don't, like a light bulb. Now one may sound a lot different but that is different.

Marketing have you convinced it is "time"? It doesn't hurt to try different tubes, preamp tubes being the most important. Lots of really old tubes are being used, like telefunken, RCA etc. I do like the GT Mullard remake.
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Re: Do Preamp Tubes in Guitar Amps Need to be a Matching Set

Post by Scodiddly » Sat Jul 05, 2008 6:46 pm

Huntlabs wrote:
acjetnut wrote:It's time to swap the tubes in my Fender Hot Rod. It uses 2 12AX7's as the preamp, and a third as a phase inverter. Do the preamp tubes need to be a matched set?
Why do you feel it is "time". Tubes basically work or they don't, like a light bulb. Now one may sound a lot different but that is different.

Marketing have you convinced it is "time"? It doesn't hurt to try different tubes, preamp tubes being the most important. Lots of really old tubes are being used, like telefunken, RCA etc. I do like the GT Mullard remake.
Nope.

Tubes do fade over time, though a lightly-loaded preamp tube can last decades. The proper thing to do is find a tube tester (sadly, you can't find them in drugstores anymore) and check all the tubes.

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Re: Do Preamp Tubes in Guitar Amps Need to be a Matching Set

Post by ??????? » Tue Jul 08, 2008 5:34 am

Scodiddly wrote: Nope.

Tubes do fade over time, though a lightly-loaded preamp tube can last decades. The proper thing to do is find a tube tester (sadly, you can't find them in drugstores anymore) and check all the tubes.
Unfortunately, drug store type tube testers don't tell you anything you need to know for operating tubes in an amplifier. They tell you basically "good" or "bad" (whatever that means) which means they test for shorts and output... at low voltages nowhere near the voltages you would need in a tube amp. And they're spotty at best, because tube testers like all other equipment need to be calibrated frequently. When's the last time you ever saw a drugstore tube tester being calibrated? You need a Hikock or other quality (several hundred dollars at a minimum) tube tester to tell you ANYTHING meaningful. Few of us have access to one of those.

Now, according to my real-world observations, preamp tubes are for all practical purposes "working or not," in my opinion. They wear very slowly and there are many vintage amps that are half-century old or more with original preamp tubes that are fine. Typically one will fail before it "wears out." Power tubes do wear faster, depending on how they are used. With proper use of standby, proper biasing, circuit topology that allows the tube to function within their parameters (i.e. not a Deluxe Reverb) etc. quality American or European (read: old stock) tubes can last a very long time indeed. In fact, I've seen many vintage 60s amps with original power tubes that still work and sound great. A power tube can be "rode hard and put away wet" and have a shortened lifespan, but that's harder to do with a preamp tube and its lower operating voltages.

Now with regards to matching preamp tubes, one thing nobody has mentioned is the fact that 12A_7 types are dual triodes, meaning they have two complete triode tubes within the same glass envelope. You CAN buy 12AX7, 12AT7 etc. with matched triodes. The only spot in a guitar amp where this would conceivably make any difference would be the phase inverter tube. And it really won't make any difference there. Save your money.

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Post by ZacharieDaquiriDoc » Tue Jul 08, 2008 7:07 am

Randy wrote:
ZacharieDaquiriDoc wrote:How does one, voice an amp?
What do you mean by that?

If you are wondering what in the amp you can change to affect the sound, it all depends on what you want. Almost everything in the amp affects how it sounds, the circuit, the speakers and cabinet style. For instance, suppose you have an amp and it's too "boomy." If it has a closed-back cabinet, you could try an open back to see if that tightens up the bass. If it is an open-back combo and it still has too much bass, you could change some capacitor values in the tone stack or on the preamp cathodes. You could simply find speakers that have less bass response. Or even more simply, you could try a different guitar and/or a different amp.
I just purchased , well guitar center advanced it, a tweedy blues jr. Jensen special design speaker. i am taking it to a local aficionado, he's going to re-bias my tubes and replace the resistors with carbon type. I want to replace the particle board cabinet with a dovetailed solid box. Someday.

2 EL 84 , 3 12AX7, he also told me replace the pre amp phase inverter tube with a 12AT7. Any thoughts or experiences with this amplifier?
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Re: Do Preamp Tubes in Guitar Amps Need to be a Matching Set

Post by GooberNumber9 » Tue Jul 08, 2008 7:13 am

??????? wrote:Now, according to my real-world observations, preamp tubes are for all practical purposes "working or not," in my opinion. They wear very slowly and there are many vintage amps that are half-century old or more with original preamp tubes that are fine.
Everyone has different gear, different ears, and different tastes. Personally, I can hear a difference in new preamp tubes after just a couple hours, and after that they are steadily changing sound in the darker direction, much like strings.

That being said, I certainly don't change my tubes or strings after a couple hours of playing time. Tubes I might change after 6 months, and I usually hold on to a set of power tubes MUCH longer than preamp tubes, one time for about eight years.

Everyone has their own tastes. I think figuring out what works for you is part of the fun of music.

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Re: Do Preamp Tubes in Guitar Amps Need to be a Matching Set

Post by ??????? » Tue Jul 08, 2008 9:05 am

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Last edited by ??????? on Wed Jan 17, 2018 9:52 am, edited 1 time in total.

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Post by Scodiddly » Tue Jul 08, 2008 4:17 pm

Granted that an emissions tube checker is not as good as a mutual conductance checker, but it's still a very useful tool. Tube sections do wear down over time (time used), and you can see it even on the "good/bad" meter of an emissions checker and tie that in with "I'm not getting as much gain as I used to" from the user.

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Re: Do Preamp Tubes in Guitar Amps Need to be a Matching Set

Post by tdbajus » Tue Jul 08, 2008 5:48 pm

??????? wrote: Or better yet, get a nice old-stock 5751, which is like a 12AX7 with only 70% the gain of a 12AX7

I've been playing with a 5751 in driver of the vibrato channel of my old '65 deluxe (no reverb) and it is a whole different animal. Signal is compressed, and the amp gets louder before distorting. It's good for some things, but I feel like I'm missing out on the dynamics some....
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