# preamp phase inverter tubes?



## SkyFire_ca (Jul 16, 2007)

hey folks, i'm not sure if this should be here or in the tech section, but i'll start here...

i'm about to re-tube both my amps, my wonderful Traynor ycv-40wr and my workhorse JCM900 4502 combo. i've been eyeballing around the tubestore and i noticed some talk about particular tubes being better for phase inverters, particularly the 5751s, i believe they were. i've decided to spend a little extra on the first 2 tubes (input amplifier and tone stack??) and get some decent jobies, i'm thinkin some Tung-sol's as they seem to be the cats-ass. however, for that final phase inverter, does it really matter? am i just as well off using the stock tubes? yes, both are running originals, "Marshall" tubes in the jcm and sovteks in the traynor. does it seem worthwhile to splurge on some decent tubes for the inverter? i doubt i'd notice the difference right now, but would there even be one?

i'm fairly sure what i'm going to get for answers, a lot of "try it with the stock first"  but that's ok. hopefully some people have tried and noticed a difference with different tubes as inverters, or maybe tried and didn't notice. really, any answer is a help.

also, if anyone feels like weighing in on the regular preamp tubes too, that'd be cool by me. expecially if the comments are along the lines of "well, for the marshall I'd prefer ..." and such. i understands the concepts and i think i get why some tubes will sound better/worse than others, so don't hold back on the technically jargon either (i love that stuff... knowledge is power, right?).

i think that's all i got for now... i'm sure there will be something similar up later about power tubes, have no fear 

... also, once the whole process is done, i'll be sure to toss some sort of review on here for those who care


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## Ripper (Jul 1, 2006)

It's good to use a high quality tube in the phase invertor. A poor phase invertor can give our harsh or wonky sound. It's the only preamp tube that really benefits from being "matched". Think of these tubes as two in one. In the normal preamp sections it doesn't matter alot if both sides of the tube don't have the same gain values, but in a phase invertor, it does make a difference. One side of the tube effects the positive side of the wave form (the sine wave your amp produces) and the other side effects the negative side of the wave. If the gain value of the two sides is drastically different, then you get a deformed wave, which leads to poor sound.

Now that being said, alot of the wave deformation is compensated for with proper biasing of your power tubes, but it is still a good idea to get a good quality tube for the phase invertor. 

Over the years I've heard a fair amount of amps sound improve just by changing the phase invertor.


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## aC2rs (Jul 9, 2007)

I purchased a complete set of JJ electronics tubes from Bob at Eurotubes for my YCV40.

http://www.eurotubes.com/


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## aC2rs (Jul 9, 2007)

Including delivery and duties, the price of the complete matched set of tubes from Eurotubes was about 60% of a re-tube with Groove Tubes from L&M.


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## Wild Bill (May 3, 2006)

Superyob said:


> Matched and graded power tubes are very important because your YCV40WR is a fixed bias amp, you have to match the tubes to the amp because you can't match the amp to the tubes.



Just a correction. The YCV40 has an automatching circuit. YOU can't adjust it but the circuit will adjust itself to each of whatever power tubes you install. It has been preset to a certain idle current. Even if you put in a hotter or colder tube the circuit will adjust to the design level.

So it doesn't matter if your tubes are matched or graded. The circuit will compensate.

Just FYI

:food-smiley-004:


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## aC2rs (Jul 9, 2007)

From personal experience I have found a good set of matched and graded power tubes for this amp will indeed make a positive difference to the sound.


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## SkyFire_ca (Jul 16, 2007)

ahhh... now that's some answers  wasn't expecting that much, or quickly. thanks to all!

I was aware that the phase inverter wasn't used to amplify the signal and was used to invert the wave form for the second power tube, but wasn't aware that both sections of the tube were used. in this case having a good tube with "matched sections" would be very important, as was stated above. this now leaves me with a very specific question as it pertains to 12ax7 vs other compatible tube types. (12au7, 12at7, 5751)
will i see a difference from these different tube types? most have lower "gain" to them, which shouldn't matter considering the function, but may lead to lower noise? i read a specific preamp tube review which suggested a particular 5751 tube was very "balanced" and would be particularly useful as a phase inverter. would that make sense? (seems to...) or would i be just as well off with a decent tube with matched sections? as is, i'll be springing for a full set of tubes for each amp, i'm looking to conserve money somewhere...

now, you folks brought up some crazy power tube questions too, way to go 
first is the one i'm fairly confident of the answer. with the jcm900, being an un-fixed bias (or however u'd say that...), am i free to use any compatible tube type for an octal socket? obvious being 5881s (stock) or various 6L6 types (6l6, 6l6gc, etc of which i'm not clear on the diffences) which should be realatively close to each other, correct? the biggest difference i can see is that some are rated at a slightly higher wattage or plate voltage (slightly over my head). if i understand correctly i could even use a kt66 tube, as they're fairly similar? possibly even switch it over to some EL34's if the transformers and such can handle the differences in voltages? i know anything other than a similar 5881 would change the character of the amp fairly significantly, especially the kt66 or el34's and would certainly involve some modifications by a competent tech, which i have available and am ok with.

and the second power tube related... if the ycv40wr is "auto biasing" or whatever... does that mean i have to use 5881s in it, as is used stock, or can it use a 6l6 type tube just as easily? my thinking being to get a more fenderish sound from the clean and more rectoish sound from the drive, what with 6l6's being the norm for these. this will probably be a similar answer to first but with the auto-biasing i'm sure it's slightly different or more involved in terms of mods.

i'm having some repairs done to both amps soon (loose jack on the marshall, various issues with the traynor) so they will both be opened up, and neither is leaving my possession soon, so mods don't concern me. i'm really just concerned with getting a sound i want and a quality i'm happy with.

again, thanks for any replies, you've all be very helpful!


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## traynor_garnet (Feb 22, 2006)

I've always heard people say they like to run a 12A*T*7 in the phase inverter even if the amp calls for as 12A*X*7 in that position.

Not sure why, but I think it helps the amp from "mushing out" when fully cranked; not sure though. Any thoughts . . .


TG


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## Geek (Jun 5, 2007)

Hi,

You can't go wrong with a GE 5751 for dynamic range, gain and tonal balance.

Cheers!


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## Scottone (Feb 10, 2006)

SkyFire_ca said:


> and the second power tube related... if the ycv40wr is "auto biasing" or whatever... does that mean i have to use 5881s in it, as is used stock, or can it use a 6l6 type tube just as easily? my thinking being to get a more fenderish sound from the clean and more rectoish sound from the drive, what with 6l6's being the norm for these. this will probably be a similar answer to first but with the auto-biasing i'm sure it's slightly different or more involved in terms of mods.


Sounds like you are looking for a different amp. A tube swap is not going to change the sound that much. If you want a Fender clean, you have to get a Fender (or something using the same circuit).


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## Ripper (Jul 1, 2006)

SkyFire_ca said:


> will i see a difference from these different tube types? most have lower "gain" to them, which shouldn't matter considering the function, but may lead to lower noise?


The gain of the phase invertor really isn't important, as long as the tube is good. As someone mentioned alot of people use 12at7 (and some amps were made that way) in the phase invertor. I've seen 12av7's used in there. It's a try and see thing.



> first is the one i'm fairly confident of the answer. with the jcm900, being an un-fixed bias (or however u'd say that...), am i free to use any compatible tube type for an octal socket? obvious being 5881s (stock) or various 6L6 types (6l6, 6l6gc, etc of which i'm not clear on the diffences) which should be realatively close to each other, correct? the biggest difference i can see is that some are rated at a slightly higher wattage or plate voltage (slightly over my head). if i understand correctly i could even use a kt66 tube, as they're fairly similar? possibly even switch it over to some EL34's if the transformers and such can handle the differences in voltages? i know anything other than a similar 5881 would change the character of the amp fairly significantly, especially the kt66 or el34's and would certainly involve some modifications by a competent tech, which i have available and am ok with.


I wouldn't be sticking in just any octal tube until I had the okay from a tech. Once an amp is set up for it, EL34's 6L6's etc can be swapped out in most amps with just a re-bias, but if you try and put an EL34 into a 5881/6L6 like say an old fender amp, look out, there are some changed that have to be made. When it comes to transformers and the power tube changes, it the voltage you need to worry about as much as it is the current draw. EL34's draw alot more current than a 6L6. If your transformer can't provide that you are in for failure.




> if the ycv40wr is "auto biasing" or whatever... does that mean i have to use 5881s in it, as is used stock, or can it use a 6l6 type tube just as easily? my thinking being to get a more fenderish sound from the clean and more rectoish sound from the drive, what with 6l6's being the norm for these.


Just because you use 6L6's doesn't mean you are going to get a recto sound. Remember too that early fenders came with 5881's and alot of fender players today still run 5881s in their amps. Power tubes are only one part of the equation to the sound of an amp, the circuit design etc plays the biggest part. If you have 5881's you can run 6L6s.


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## Wild Bill (May 3, 2006)

SkyFire_ca said:


> ahhh... now that's some answers  wasn't expecting that much, or quickly. thanks to all!
> 
> I was aware that the phase inverter wasn't used to amplify the signal and was used to invert the wave form for the second power tube, but wasn't aware that both sections of the tube were used. in this case having a good tube with "matched sections" would be very important, as was stated above. this now leaves me with a very specific question as it pertains to 12ax7 vs other compatible tube types. (12au7, 12at7, 5751)
> will i see a difference from these different tube types? most have lower "gain" to them, which shouldn't matter considering the function, but may lead to lower noise? i read a specific preamp tube review which suggested a particular 5751 tube was very "balanced" and would be particularly useful as a phase inverter. would that make sense? (seems to...) or would i be just as well off with a decent tube with matched sections? as is, i'll be springing for a full set of tubes for each amp, i'm looking to conserve money somewhere...


Where did you get the idea that the phase inverter has no gain? Most guitar amps used a circuit called a "long tail" which has HEAPS of gain! There are unity gain phase inverter circuits used in some early vintage amps but since the late 50's pretty well all guitar amps use the long tail gain phase inverter, with only a few exceptions.

Still, most amps have far more gain than needed to drive the final tubes to full power. The extra gain just shows up as distortion, but that's a GOOD thing!:smile:

So trying lower gain tubes in the PI can give you a better clean sound and perhaps more head room. I wouldn't worry too much about "balanced" 12AX7's unless you're more of a jazz player wanting SUPER clean! The longtail circuit is inherently unbalanced by design and some parts values for one section of the tube are changed to compensate. Unless you have a tube so unbalanced that really it should be replaced you probably would WANT to have a stock 12AX7 in that position! Balanced 12AX7's are a hifi thing and not a rock and roll thing. Again, unless you're a jazz player who would want a hifi sound? You'll never sound like Eddie Van Halen or Yngwie that way!



SkyFire_ca said:


> now, you folks brought up some crazy power tube questions too, way to go
> first is the one i'm fairly confident of the answer. with the jcm900, being an un-fixed bias (or however u'd say that...), am i free to use any compatible tube type for an octal socket? obvious being 5881s (stock) or various 6L6 types (6l6, 6l6gc, etc of which i'm not clear on the diffences) which should be realatively close to each other, correct? the biggest difference i can see is that some are rated at a slightly higher wattage or plate voltage (slightly over my head). if i understand correctly i could even use a kt66 tube, as they're fairly similar? possibly even switch it over to some EL34's if the transformers and such can handle the differences in voltages? i know anything other than a similar 5881 would change the character of the amp fairly significantly, especially the kt66 or el34's and would certainly involve some modifications by a competent tech, which i have available and am ok with.


Be careful here! Scottone and Ripper are giving you good advice about changing so much you might as well get a different amp! It is possible to put a Chevy engine in a Ford car but I would much rather have YOU pay for it than me!:smile:

Besides, tube differences are not as great as the salesguys tell you when they are trying to get you to buy THEIR tubes! I know guys swear that they can tell the difference when they change them but it's rarely a real test. You can't swap them in and then make up your mind. It's too easy to fool yourself. You need to be blindfolded and have SOMEONE ELSE swap the tubes (re-biasing each time!) to be fair and true.

There are indeed CRAP tubes but that's a different story.



SkyFire_ca said:


> and the second power tube related... if the ycv40wr is "auto biasing" or whatever... does that mean i have to use 5881s in it, as is used stock, or can it use a 6l6 type tube just as easily? my thinking being to get a more fenderish sound from the clean and more rectoish sound from the drive, what with 6l6's being the norm for these. this will probably be a similar answer to first but with the auto-biasing i'm sure it's slightly different or more involved in terms of mods.


You can use 6L6 types safely. The reason is that the 5881 has a bit lower plate dissipation figure, more like an EL34. This means that for the same voltage on the plate the idle current must be a bit lower than for a 6L6. Since the Traynor was designed around the 5881 the autobias circuit will bias the 6L6 a bit on the cold side, thinking it's a 5881.

If the amp had been designed for 6L6's it wouldn't be a good idea to let an autobias circuit set the idle current for 5881's. You'd end up too high and could stress the tubes.



SkyFire_ca said:


> i'm having some repairs done to both amps soon (loose jack on the marshall, various issues with the traynor) so they will both be opened up, and neither is leaving my possession soon, so mods don't concern me. i'm really just concerned with getting a sound i want and a quality i'm happy with.


The Traynor is a modern printed circuit board amp. You can only do the simplest of mods 'cuz you can't easily change connections and circuitry when the "wires" are actually traces of copper on an epoxy board, which of course can't be moved. This is just a fact of life with non-handwired amps.

This is why so many guys get so involved with swapping different brands of tubes trying to get a better sound. Any real tech can change the value of one capacitor in the tone stack and change the tone far more than changing tubes ever will! It's not just that they don't know how to change things in the circuit. Even their tech will find it a PITA or even impossible! You either get a HUGE bill or be told it just can't be done.

I suspect this is one of your first amps. We all go through the stage where we think in terms of getting all the different tones in the world from our one amplifier. It's like when we first get to drive the old man's car and we want to buy stuff from a high-performance shop. We end up with an old man's car that somebody bolted on some performance stuff! It just doesn't really go any faster!

Any "universal" tool tends to work half-assed at EVERY job! Carpenters have different sizes of saws and hammers in their kit. Guitarists are the same. If you want the largest variety of tones you need at least two guitars (one humbucker/Gibson and one single coil/Fender) and a couple of different sounding amps. You can blow a lot of money buying all kinds of stuff and not really end up with much of value.

You've got a nice little amp there. Let it do its job! If you want a Marshall/EL34 sound then get another amp designed to do that tone well!

Just MHO...

:food-smiley-004:


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## SkyFire_ca (Jul 16, 2007)

again, tonnes of great responses, you folks are awesome!
lemme recap a little here, make sure i follow...
the phase inverter "is" used for gain, so the standard rules of preamp tubes apply just as strongly as if it were any other preamp tube? (basically) and unless mine are shot, i might as well use the ones i have, unless i want to experiment?

as for powertubes, in the traynor i'm best keeping the 5881 type tubes or trying some 6l6's if i'm ok with a slightly "colder" bias? (doubt i'd notice) and as for the jcm, it's not fixed, so have fun as long as the tech says "go" and i like the price? hehe

i understand the comments on gear and getting what i really want, i've thought about those kinds of things an absolute tonne... I'm already reasonably armed for guitars, decent epi LP copy and a wonderful mid-80's MIJ fender strat. and amp wise i'm doin ok... a decent marshall and a nice traynor which approximates a fender clean well enough for my ears.
it sounds like the traynor is actually the worse testbed to try things on, it might be a little more limited in it's options, which is just fine by me, i like it how it is, i was just hoping some different tube types might bring out a little more chime or what not. realistically i need to reign in the bass on it, as it's can really get boomy. if that's my goal i'm probably better off letting my tech tweak the tonestack? o well, i think that traynor will take care of itself once i get going...
the marshall is the real problem, it's been the largest love/hate relationship i've ever been in. i bought it on a whim for more than i should have, not realizing the value of these 900's... i'd just gotten back into playing after about a 5yr break, being out of touch does strange things. i think i was looking for the sound of a roaring modded 800 stack, and got a little wheezy thing... I've since learned my way around it, but i'm regularly disappointed by it. I've got no interest in selling it, as i really can't get enough out of it to justify the effort, and not enough to purchase a suitable replacement, that's for sure. I'm at the point of tweaking it to get what i want. right now, that's more bottom end, maybe a little more focused bass response, a little more mid cut and a lot more top-end sizzle. Oh, and lest i forget, less fizz, way less fizz, and more crunch 
there, have i said too much again? when did this turn from a tube discussion into an amp debate?  if that's the trend though, anyone with more knowledge of these jcm900's, feel free to pop in, i'd love to have your thoughts on modding this circuit. specifically feelings on switching over to something really odd, tube wise, no 5881's or 6l6's, more like EL34 switch or maybe KT66's or what not? if i understand from above the EL34's might be decently similar to the 5881's?
yup, i'll shut up now... sorry for the long posting again


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## Kapo_Polenton (Jun 20, 2007)

I found a difference in preamp tube positions and do use matched output tubes.. however, I don't use a balanced tube for the phase inverter. A lot of guys don't bother doing this so you'll find as many people who swear by it as people who don't. The number one thing you must do though, is BIAS the amp for each new set of tubes!


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