Phase inverter tube?

[888guitars]

Is there such a thing as a specific 12ax7 designed or "matched" for the phase inverter position?

[daz]

Is there such a thing as a specific 12ax7 designed or "matched" for the phase inverter position?

Not specifically made for it, no. However, some dealers do test them to find those who;s triodes are matched and then sell them for a premium for the purpose of using in the PI. However, a matched tube doesn't insure a matched output because the components of the PI also need to be just right, and components vary to a degree that you aren't likely to have a matched circuit. I'm no expert, but i think if a balanced PI is what u r after it would be best to put a balance pot in it so you can use any tube and have balance.

[g1]

By design they should be matched within a certain tolerance. As Daz mentioned, no point matching the 2 sides of the phase splitter unless all the components of that circuit are also balanced. Then there is the whole question of whether you really want perfectly symmetrical clipping in a guitar amp.
But aside from all that, many tube vendors do offer this kind of matching of triode sections. Here is an example:
www.thetubestore.com - Matched Sections Service

[888guitars]

Well I just saw a jj 12ax7 that was specific to a phase position. I thought it seemed fishy? A lot of amps even try to not balance the inverter for a bit of asymmetric output?

[g1]

Yep, but guys with tube hifi stereo systems might want matched phase splitters.
Edit: only if it costs extra .

[Enzo]

Well I just saw a jj 12ax7 that was specific to a phase position. I thought it seemed fishy? A lot of amps even try to not balance the inverter for a bit of asymmetric output?

Where, link us to it. Sure it wasn;t a recommended for PI tube? I have a hard tome thinking JJ made a tube specially for PI use.

As was said by others, you can pay extra for a "balanced" 12AX7 - the two sides have more or less the same gain. But unless you precision match all the other parts in your power amp, it won;t achieve anything.

In hifi amps, the goal is super accurate reproduction of the input, so the concept of a balanced tube at least makes some sense, but there still is the thing about precision in all the rest of the parts. In guitar amps, hifi is NOT the goal of the amp. The goal is to make a pleasing sound when played through.

These days, I am sure someone has decided on some very specific amounts of unbalance sounds good. But for the most part, amp makers are not TRYING to make unbalanced power amps, they simply don;t try to MAKE them balanced.

[soundguruman]

Is there such a thing as a specific 12ax7 designed or "matched" for the phase inverter position?

Yes there is, but it generally don't work as advertised.
You can pick out a tube with "matched" sections...
But the amp does generally not provide equal signal or equal loading to both sections, so the result is that you still get UN-equal drive, and UN-equal clipping at the power tubes--even though the PI is supposedly "matched."
Many amps have UN-equal PI plate resistors...
Also most "matched" sets of power tubes are not very closely matched either.
And also, most output transformers do not have closely matched windings either.
So whatever "matched characteristics" are lost due to other factors. You hear NO difference at all, in most cases for sure.

Testing with a scope, go thru 4-5 PI tubes and pick out one that produces (about) equal clipping, in "a given" amp. But the one that produces equal clipping will NOT have "matched" sections. It will have UN-equal sections. Try this yourself.

A better strategy is to install balancing pots for PI drive, bias, or power tube balance....then you could actually balance it out, more or less.
So, when we talk "matched" sections in a PI, the end result is essentially a myth.
You can pick out a "matched PI," but the rest of the amp is anything but matched or balanced. What did it achieve? Nothing.

Can you really HEAR when the output is matched, producing equal clipping? Most people cannot hear it.

[888guitars]

I had a customer bring in his Engl fireball and brought in jj tubes and the box had one labeled phase inverter/matched or something like that. This is what started this question. I may still have the box. I will take a pic and post it.

[Enzo]

OK, that was just a selected tube. They take a pile of 12AX7s, and measure the gain of the two sides of each. The ones that are close to being the same are considered "balanced", and they set them aside and label them. They are just plain old regular 12AX7s that just happen to have the two sides the same. They are not specially made or anything. But they do charge a little more for them.


You can also buy tubes selected for other qualities. For example, they plug the 12AX7s into an amp circuit. They listen. Some have less noise than others, so they set those aside and charge a little more for "selected for low noise". And they also tap on them to find any that are less microphonic than the rest, and you guessed it, they set those aside and charge extra for "selected for low microphonics".


Imagine you are at the grocery store, and you look over the tomatoes for one with no bruises. You pick one that looks better than the rest. That tomato was not special grown,l it just happened to be the best looking tomato in the bunch. SO you chose it - "selected for low bruising."

[soundguruman]

I had a customer bring in his Engl fireball and brought in jj tubes and the box had one labeled phase inverter/matched or something like that. This is what started this question. I may still have the box. I will take a pic and post it.

It's a gimmick, I donno who's idea it was to start doing it.
Somebody with little knowledge of tube amps, trying to exploit gullible customers...
But lots of people have fallen for it.

Generally, if the amp has 5 preamp tubes, you can trade them around, and find one that produces equal clipping in a particular circuit.
So, buying a "matched" one is rather silly.

I had a customer who ordered one from Voodoo, made a big deal out of it, paid a lot to get it...
I didn't have the heart to tell him he was being fleeced...

[soundguruman]

Yep, but guys with tube hifi stereo systems might want matched phase splitters.
Edit: only if it costs extra .

There ARE hi fi circuits with carefully matched sections, and that's the only place that something like this would actually produce a result.
BUT, can you really hear a difference??? most people could not, I'm quite sure.

[Chuck H]

Unless the anomalies of a mismatch are made evident it doesn't matter if a PI tube is matched. Let me qualify that...

Most players rarely push their amp to where any mismatch in the PI tube, circuit or power tubes even matters! And anyone who does may prefer a mismatch to a match. Blind studies HAVE been done (though I'm not inclined to search for links). A mismatch is generally preferred!!! matched PI tubes are in fact almost never necessary for HiFi use since the same usage MO applies. With light use, if a slightly mismatched PI tube produces an extra .05% distortion on the 2nd harmonic it probably would go unnoticed for average listening. But give 'em what they want! If a customer believes his amp will sound better with a matched tube then put it in there. They'll listen and say they can hear it and how good it is. They might use terms like "sound stage", "midrange depth" or "note separation". Let them have it! It makes them happy players. And happy players play better and are happier with your services. But DON'T pretend you buy into it. Don't dispute it either. Wherever the customer ultimately lands on the issue isn't up to you and you shouldn't have to be accountable for their ignorance.

FWIW WRT the PI tube in guitar amps I'm with SGM... Plug different tubes in until one sounds good with a particular amp. Works every time. But it doesn't have a thing to do with matching or balancing. Your customer won't want to hear that though

[soundguruman]

Unless the anomalies of a mismatch are made evident it doesn't matter if a PI tube is matched. Let me qualify that...

Most players rarely push their amp to where any mismatch in the PI tube, circuit or power tubes even matters! And anyone who does may prefer a mismatch to a match. Blind studies HAVE been done (though I'm not inclined to search for links). A mismatch is generally preferred!!! matched PI tubes are in fact almost never necessary for HiFi use since the same usage MO applies. With light use, if a slightly mismatched PI tube produces an extra .05% distortion on the 2nd harmonic it probably would go unnoticed for average listening. But give 'em what they want! If a customer believes his amp will sound better with a matched tube then put it in there. They'll listen and say they can hear it and how good it is. They might use terms like "sound stage", "midrange depth" or "note separation". Let them have it! It makes them happy players. And happy players play better and are happier with your services. But DON'T pretend you buy into it. Don't dispute it either. Wherever the customer ultimately lands on the issue isn't up to you and you shouldn't have to be accountable for their ignorance.

FWIW WRT the PI tube in guitar amps I'm with SGM... Plug different tubes in until one sounds good with a particular amp. Works every time. But it doesn't have a thing to do with matching or balancing. Your customer won't want to hear that though

OH, OK

FOR SALE: matched phase inverter tubes. Specially selected to give perfectly ballanced drive, in tube amps.
1X 12AX7 = ONLY $49.95 + 15.95 shipping!!! Special limited quantity sale!
Buy yours today!

Is that better?

[Chuck H]

OH, OK

FOR SALE: matched phase inverter tubes. Specially selected to give perfectly ballanced drive, in tube amps.
1X 12AX7 = ONLY $49.95 + 15.95 shipping!!! Special limited quantity sale!
Buy yours today!

Is that better?

I'll need a dozen. Do I get to pay shipping on each of them? I wouldn't want anyone to think I went the cheap route!

[Leo_Gnardo]

I had a customer who ordered one from Voodoo, made a big deal out of it, paid a lot to get it...
I didn't have the heart to tell him he was being fleeced...

Well that's Voodoo doodoo for you, and the people who believe. How many of my customers - I've had to set them AND their amps straight. "Welll if he charges more, he oughta be good, right?" No-o-o-o-o-o-o-o-o !!!!!

If you even mention Dumble, Voodoo will Dumble-ize the amp under repair, his own way, and charge an extra $1150. This is without the customer specifically mentioning they want the mod. The guy's out of control.

What's worse is his name is similar to mine, and he's also in NY. I just hope people don't ever get us confused.