Preamp tubes - when to buy "balanced" and/or "matched"?

[Jon Silberman]

Many tube perveyors offer balanced and/or matched preamp tubes at a premium price. Can someone help me understand when and why, for regular-type V1-V3 applications (i.e., excluding phase inverters and trem or reverb drivers), it is preferable to go with a matched, balanced, or matched and balanced preamp tube? Thanks.

[Blue Strat]

Never for any other position than the PI tube, and there's a lot of controversy about the benefits in the PI slot.

It's typically misunderstood that balanced means DC balance (which most tube testers don't test for) and only has meaning in a phase inverter socket. AC or gain balanced (both sides of the tube are capable of exactly the same amount of amplification, ie "gain") can be important in non PI stages of stereo equipment where the triodes of each tube are split between left and right.

[Jon Silberman]

Thanks, Mike.

I actually need to take my own advice to so many others: use the search function! This has been discussed before here and I should have searched for it before posting but many thanks nonetheless for your additional guidance now.

http://www.google.com/search?domains=www.thegearpage.net&sitesearch=www.thegearpage.net&ie=ISO-8859-1&oe=ISO-8859-1&q=%22balanced+tubes%22

[Blue Strat]

Thanks, Mike.

I actually need to take my own advice to so many others: use the search function! This has been discussed before here and I should have searched for it before posting but many thanks nonetheless for your additional guidance now.

http://www.google.com/search?domains=www.thegearpage.net&sitesearch=www.thegearpage.net&ie=ISO-8859-1&oe=ISO-8859-1&q=%22balanced+tubes%22

I've forgotten if there was a "conclusion" in that thread, I bailed when the bickering got too heavy. As with most controversial topics, you'll get a host of participants repeating what they've read somewhere on the internet without really understanding the fundamentals.

[John Phillips]

IMO the only time to use a balanced tube is in the phase inverter (or parallel driver, eg Marshall Major) slot in an amp where you've already tried one and prefered the tone that way, and probably assuming you haven't also changed the power tubes in the mean time - which also affects the final balance of the output waveform if they're not perfectly matched (which they almost never are, even in new matched sets). Anything else is a waste of time and money, because in almost all other applications the two halves of the tube are used completely independently and their performance has no bearing on each other. Not even in the reverb driver in a Fender, where both halves are simply summed.

By all means, try one in the PI if you want, and if it does sound better to you, then keep doing it. It's also worth trying unmatched tubes to see whether you like the particular imbalance too, as there's nothing to say (and some good evidence against) that a perfectly balanced output section sounds best for guitar anyway. The bad news is that if you find a particularly great sound with an unmatched tube, you may never be able to duplicate it...

[rockon1]

Basically never.

Kevin Ocorror on the subject:

: What's the deal with matched tubes? Some experts say they're very important, and these days it doesn't seem to be too expensive to get matched tubes. Then they talk about matched preamp tubes, and I don't know where to get those.

A: You don't need matched tubes of any kind in your guitar amp. If you are trying to achieve vintage Fender, Marshall, Vox, Silvertone, Gibson et al. tones, then you simply plug in the tubes you have, check the bias and play. No manufacturer of musical instrument amps uses matched tubes, with the possible exception of Groove Tubes.
As discussed in the TUT-series, matched tubes will drift out of balance over time due to electrical imbalances in the circuit and the different response of each individual tube to mechanical stimulus. Drop the amp and one tube may break while the other survives, even though they were electrically "matched" when you bought them.
As discussed in this FAQ and in our books, asymmetries in the push-pull output stage, and in the handling of the signal throughout the signal path, contribute to the harmonic balance and thus the warmth of the tube amp's sound. You can build in specific asymmetries, or use unmatched tubes or even different tube types to play with asymmetry.
Matched triode sections are often cited as "beneficial" in the Schmitt splitter used in most guitar power amps. The circuit is inherently out of balance and has skewed values to restore some semblance of output signal balance. Perfectly matched triodes would offer no actual benefit and would contribute to higher levels of odd-order harmonic distortion. These sound "crisp" in small quantities but are "harsh" in large levels. Again, just as with separate output tubes, the two sections of a dual triode will be quite

[Jackie Treehorn]

Never for any other position than the PI tube, and there's a lot of controversy about the benefits in the PI slot.

It's typically misunderstood that balanced means DC balance (which most tube testers don't test for) and only has meaning in a phase inverter socket. AC or gain balanced (both sides of the tube are capable of exactly the same amount of amplification, ie "gain") can be important in non PI stages of stereo equipment where the triodes of each tube are split between left and right.

A bit off topic, but can you AC match the triode sections of 2 different 12bh7's?

[Blue Strat]

Basically never.

Kevin Ocorror on the subject:



Yeah, the same guy who said it's fine to use 360 Plate Volt maximum tubes (6V6s) in a amps with 470V on the plates (Twin Reverbs).

[rockon1]

Yeah, the same guy who said it's fine to use 360 Plate Volt maximum tubes (6V6s) in a amps with 470V on the plates (Twin Reverbs).


Dont know about that. However there are some respected guys right on this board that would agree a balanced PI is unnecassary and even pointless.

[Blue Strat]

Dont know about that. However there are some respected guys right on this board that would agree a balanced PI is unnecassary and even pointless.

Yeah, but part of your Kevin O post was talking about power tube matching which is a completely different topic.

[Blue Strat]

A bit off topic, but can you AC match the triode sections of 2 different 12bh7's?

Sure, if you have about 20 random tubes to start with. That's just a guess, but probably pretty close depending on how close you want to get.

[fullerplast]

I always end up making the same point on these PI threads.... When you swap a PI tube in an inherently unbalanced (or even in a balanced) PI circuit, you have only three cases to consider: you will cause the PI circuit output to be 1) more unbalanced than before, 2) less unbalanced than before, or 3) the same as before. Since all three will likely sound different from one another, it is an issue worth considering.

If you like the way the amp sounded before, then you would want to replace the PI tube with one that had the same relative balance between halves. The easiest way to do that consistently from the start is with matched tubes.

If your favorite PI tube is unmatched, then you would at least want the replacement to be unmatched in the same direction. You can do this with your ears or with a tube tester but it is worth doing IMHO.

[Jackie Treehorn]

Sure, if you have about 20 random tubes to start with. That's just a guess, but probably pretty close depending on how close you want to get.

Ha ha! Yes, I meant can YOU match them and sell them to me.:BEER

(I figured it was hypothetically possible)

[Chris Scott]

IMO the only time to use a balanced tube is in the phase inverter (or parallel driver, eg Marshall Major) slot in an amp where you've already tried one and prefered the tone that way, and probably assuming you haven't also changed the power tubes in the mean time - which also affects the final balance of the output waveform if they're not perfectly matched (which they almost never are, even in new matched sets). Anything else is a waste of time and money, because in almost all other applications the two halves of the tube are used completely independently and their performance has no bearing on each other. Not even in the reverb driver in a Fender, where both halves are simply summed.

By all means, try one in the PI if you want, and if it does sound better to you, then keep doing it. It's also worth trying unmatched tubes to see whether you like the particular imbalance too, as there's nothing to say (and some good evidence against) that a perfectly balanced output section sounds best for guitar anyway. The bad news is that if you find a particularly great sound with an unmatched tube, you may never be able to duplicate it...


John- If you EVER want to vacation in the tropics, please consider Costa Rica- warm weather, lush tropical habitat, beautiful women, and a budding amp tech who PROMISES he won't keep you in the shop more than 4-5 hours a day.........

[Old Tele man]

Sure, if you have about 20 random tubes to start with. That's just a guess, but probably pretty close depending on how close you want to get....unless you're talking NOS tubes, I'm betting you'd need a "pool" of about ten-times that number (~200) of todays' imported tubes before you'd find one with truly "matched" halfs!

...can you say "pessimist?"

[Blue Strat]

Ha ha! Yes, I meant can YOU match them and sell them to me.:BEER

(I figured it was hypothetically possible)

Sure is. If you're serious, I do business at my email address or phone.

kcanostubes@verizon.net

[Blue Strat]

I always end up making the same point on these PI threads.... When you swap a PI tube in an inherently unbalanced (or even in a balanced) PI circuit, you have only three cases to consider: you will cause the PI circuit output to be 1) more unbalanced than before, 2) less unbalanced than before, or 3) the same as before. Since all three will likely sound different from one another, it is an issue worth considering.

If you like the way the amp sounded before, then you would want to replace the PI tube with one that had the same relative balance between halves. The easiest way to do that consistently from the start is with matched tubes.

If your favorite PI tube is unmatched, then you would at least want the replacement to be unmatched in the same direction. You can do this with your ears or with a tube tester but it is worth doing IMHO.

Yep, I've said this a number of times myself. They DEFINITELY can make a difference, but what sort of difference depends on many variables. ;)