how much difference does a matched set make?

[bigred1025]

I have a Mesa Boogie Bass 400+. It takes 12 6L6 power tubes and, like most Mesas, has no bias (self biasing.) Only one tube is bad. I bought them all together as a matched set but wonder if I will do damage to the amp by only replacing the one bad one. Anyone know? Also, where is a good online place to buy a replacement set if need be? Thanks.

[Enzo]

Most any good seller can make up a set of 12, pretty close if not real match. And it depends on what each considers "matched." 5%-10%-20%? For example Groove tube sells their tubes "graded" into 10 levels - I think. I don't really know what each level really equates to, but they do it. That means that WHATEVER the whole range might be, all their tubes are lumped into 10 grades. And they have a spiel for each grade to make it appealing to you. On the other hand, the identical tubes when sold through Fender - Fender Groove Tube - the tubes are broken down into only three grades - red, white, or blue. And I have zero idea what each of those means. But though they are more or less matched, it is far less precisely than the 10 grade system. And both are from Groove.

But assuming that match really does mean something, you shuold realize that most amp makers do not bother with matching tubes. It most certainly will not HURT your amp to have an odd tube in it.

And whether you would hear a difference betwen matched tubes and random ones is hard to say. Someone might, and a lot of people won't. Especially in a set of 12. In a set of two, one side way off from another would be more noticable than in a set of 12, where the six on each side will tend to average out. The sonic difference of a matched set will be subtle. The main advantage to me is that matched sets are more likely to balance the amp, and that means B+ ripple wil cancel out in the power stage. That means unmatched tubes will add more hum in the power stage than matched. Not tons, but can be noticable.

[Steve Conner]

If you bring the amp to a good tech who has some tubes in stock, he might be able to find you a tube from his stash that is a reasonable match to the 11 you already have.

If it was my own amp, I'd just get another tube of the same make and type, and stick it in there. The worst it can do is draw more idle current than the others, and start redplating, in which case try another one. Enzo already explained about the grading system that Fender/Groove Tubes use, so if you have Groove Tubes in it, you can probably just order another single tube of the same grade.

[stokes]

What tubes are you using?If you are using tubes that are graded by Mesa or GT you can get one that will match the rest.

[Jammin'John]

Yea,just put 1 tube in and it'll work fine !

JJ

[jeffinwv]

are not mesa tubes made in china?

ive had a few buddy get those and it seems they came with made in china stickers on them.

i had two friends grab two mesas and put in an amp and they didnt sound as good as the 30 year old ones that were in there...and the mesa were new!

[Enzo]

SOme Mesa tubes are Chinese and some are not. Their tubes do not all come from the same place.

[jrfrond]

Ah, the old tube-matching controversy. This all depends on who you speak to.

OK, so I am fairly new around here, but being in the business 30+ years kinda makes me an old-timer, or at least an old warhorse! If you talk to guys like me, we will tell you that matching means squat, and that unmatched sets might even SOUND better, because the tubes will clip at different levels and lend their own harmonic qualities to the signal. In addition, ALL of the tubes we regard as "sacred" e.g. RCA 6L6, Tung-Sol 5881, Mullard EL34, etc. were NEVER matched by tube manufacturers. The amps sounded great and they lasted (the amps AND the tubes that is).

Now, of course, no push-pull tube amp has perfect symmetry anyway, so asymmetrical clipping, which is what makes more amps interesting, always exists to some degree. So, is tube-matching an attempt to remove that variable from the overall equation? I can tell you this: many tubes I receive as matched in my shop DON'T match, even though they are labeled as such, and also, tubes don't necessarily age at the same rate either. Therefore, if they match when new, after a few weeks, they might not match at all.

Of course, you can argue this from the technical side, but when all is said and done, it's about TONE.

Truth or fiction? I have my own theories.

[Jammin'John]

I agree.
Guitar amps have more of an interesting and thicker sound when the tubes aren't perfect.
In the old days you just popped a tube in and as long as it didn't hum a lot you were good to go.
I think the Hi Fi guys are the folks who are anal about this.
JJ

[Rob Mercure]

I'm in general agreement with most comments, but: Let's not mistake "static" 0 DC - "match" for "dynamic" match. While dynamic mismatch may sound good static mismatch may be large enough to DC saturate one side of an OT primary and/or cause other mischief as a system melts. One tube out of 12 probably ain't gonna make that much difference.

Secondly one of the reason that the "sacred" tubes were not matched (and every manufacturer I know of did offer "matched" sets - and I remember buying them for HiFi enthusiasts 35 years ago or so - was that overall tolerances were better. Assembly lines had been in place for generations, engineers were trained in tube technology and didn't learn it "post graduate" on-the-job, and materials were better sourced with, again, generation old mica spacer fabricators for example. So there was much less need for matching as a greater number of tubes came off the assembly line "matched."

[Enzo]

The amp makers don't bother to match tubes, but I prefer them for hum balance reasons. it is a small thing for sure, but I like it. That is what the bias balance control on Fenders was for, balancing the current through the OT.

I have an old B18X Portaflex Ampeg at home. The last pair of 7027 I bought for it was RCA 7027MP. Factory matched pair. I suspect RCA was not just scamming me, I think they really did match them up in some fashion.

[TD_Madden]

As an aside, I don't think any Mesas are "self-biasing"...they are non-adjustable fixe-bias.

[Enzo]

In marketing-speak, that's what self-bias means these days.

Customers have been brow beat with the "bias must be adjusted at all costs" mantra for so long, they expect it. So saying an amp has non-adjustable bias is a turn off, but self-bias sounds like a good feature.

When I hear "self-bias," I get a mental image of an amp that somehow senses current and then a servo circuit adjusts voltage to compensate.

[jrfrond]

In marketing-speak, that's what self-bias means these days.

Customers have been brow beat with the "bias must be adjusted at all costs" mantra for so long, they expect it. So saying an amp has non-adjustable bias is a turn off, but self-bias sounds like a good feature.

When I hear "self-bias," I get a mental image of an amp that somehow senses current and then a servo circuit adjusts voltage to compensate.

I just LUVVVVVV marketing, don't you? :rolleyes: :D

I attend NAMM every year as part of my business. Let me tell you, they sure do pile on the bullshit to sell the same ol' stuff year after year. :eek:

Enzo, your comment "Customers have been brow beat with the "bias must be adjusted at all costs" mantra for so long, they expect it" is interesting, because it is tangent with the whole "matched tube" thing.

When we service SS power amps, we either match output transistors ourselves, or purchase matched sets from the manufacturers we service (Crown, QSC, etc.). When a device, such as an output transistor, is current-operated, and handling A LOT of current at that, you MUST make sure that the current-sharing characteristics are in tight tolerance, or you can have a catastrophic meltdown on your hands. But power tubes? Man, I just do NOT totally buy into it. To a point perhaps, because of the widely-varying quality control of newly-manufactured tubes, but as long as the tubes are GOOD, there will not be any meltdowns of tube amps due to the use of unmatched sets of power tubes. In 30+ years, I've NEVER had a comeback due to unmatched tubes when I did use them. I HAVE had MANY cases of a single tube in a matched set going nuclear however. Again, it's all marketing. We can thank Aspen Pittman (Groove Tubes) for that.

[Jammin'John]

I NEVER buy groove tubes.
It's a bunch of crap.
Like his GE tubes that are made in CHINA !

JJ

[bob p]

As an aside, I don't think any Mesas are "self-biasing"...they are non-adjustable fixe-bias.
i could have sworn that Mesa made some cathode biased amps. maybe my memory is playing tricks on me.

[Jammin'John]

I think the Blue Angel is cathode bias.
Kevin Eubanks on the Tonite Show plays one.

JJ

[kg]

i played for over a year with 1 of the 6 kt90s in one channel of the BAGA pulled. its screen resistor had opened up and i hadn't fixed it.

when i DID end up fixing it, and using the full sextet again in that channel, it sounded just like it did before. ;)

i have not heard a hell of a lot of difference in noise/hum when twiddling with bias balance in a pp output stage. i think the unbalance has to be ridiculous before things get really noticeable.

[stokes]

A slight mis-match is okay,and in fact will give a better sounding output,but if one tube is drawing 20ma's and the other is drawing 35ma's the hum will drive you nuts,in a two tube output.Of course if you are talking about a 12 tube output section,one tube isnt going to make much of a difference,since you are talking about the average draw of six tubes on one side vs. the average of six on the other.

[J Martin]

There are good reasons to use matched tubes. One reason I did not see mentioned is that the extra handling the tubes get during the matching process reduces the drop out rate to near zero. I buy a lot of tubes and while the vendors make good on bad tubes, the whole return process is a real pain and takes time away from work. Also I have found matched tubes make the repairs more consistant and biasing easier. Tubes will drift anyway and its nice to know they are drifting from the same value and none will end up too far off.

[kg]

A slight mis-match is okay,and in fact will give a better sounding output,but if one tube is drawing 20ma's and the other is drawing 35ma's the hum will drive you nuts,in a two tube output.Of course if you are talking about a 12 tube output section,one tube isnt going to make much of a difference,since you are talking about the average draw of six tubes on one side vs. the average of six on the other.

the amount of mismatch that will produce a hum voltage at the speaker terminals also depends greatly on your power supply. in fact with a "perfect" b+ rail you don't need the PSRR that differential operation gives you at all. :)

[Steve Conner]

Mismatched tubes will draw unequal idle currents through the two halves of the OT primary, which will cause a net DC magnetization of the core, making it saturate early on one polarity. I don't know how ordinary O.T.s like this, but I know toroidal ones cope very poorly with it.

[telemoxy]

In marketing-speak, that's what self-bias means these days.

Customers have been brow beat with the "bias must be adjusted at all costs" mantra for so long, they expect it. So saying an amp has non-adjustable bias is a turn off, but self-bias sounds like a good feature.

When I hear "self-bias," I get a mental image of an amp that somehow senses current and then a servo circuit adjusts voltage to compensate.

Just out of curiousity, oes anyone know how the self biasing circuit in a Traynor YCV50 "Blue" works? The idea behind it is that you don't need to use "matched tubes".

[Enzo]

Chances are it is nothing cosmic. SInce unmatched tubes will work fine in an amp anyway. For example the PV arrangement where tubes are simply biased real cool, so prtty much whatver you stick in there will not be underbiased.

Got a schematic?

[telemoxy]

Chances are it is nothing cosmic. SInce unmatched tubes will work fine in an amp anyway. For example the PV arrangement where tubes are simply biased real cool, so prtty much whatver you stick in there will not be underbiased.

Got a schematic?

Yes.

http://www.traynoramps.com/default.asp?p1=7&p2=0&p_id=30

See the All Tube Guitar Combos under YCV50Blue and click on the "download" link in the service manual column and a pdf is downloaded. The schematic is included on page 6 to 9. It looks a bit cosmic to me.

[Steve Conner]

It looks like a totally ordinary setup with a pot to adjust the bias. They even printed "Bias 350mV across R91 and R92" on the schematic.

There are lots of transistors, op-amps, MOSFETs and other junk in there, but they don't seem to have anything to do with the bias.

[Enzo]

Looks utterly conventional to me, I don't know why this would be any more self biasing then an old Fender Twin Reverb or a MArshall.

[telemoxy]

It looks like a totally ordinary setup with a pot to adjust the bias. They even printed "Bias 350mV across R91 and R92" on the schematic.

There are lots of transistors, op-amps, MOSFETs and other junk in there, but they don't seem to have anything to do with the bias.

Quite right. In comparing the schematic at this link to the one I have it appears they have made changes. They have removed the auto-biasing. Pity! It allowed quick swapping of output tubes. If you or Enzo are interested I could email you the schematic with auto-biasing.

[voxrules!]

I HATE marketing ( or at least the current concept of marketing, which is something jrfrond explained perfectly : invent all sort of b*@°#!!t to sell whatever kind of crap at all costs! ) - The truth is, as some of you have already pointed out, that when it comes to tube ( or should I say valve, being on the other side of the Atlantic Ocean ) amps, most of the times unmatched pairs actually sound better to the musicians' ears, we all know most of the amps out there in the REAL world are class AB1 amps, so a perfectly matched set would eliminate completely all even-order harmonics; still some tube-badgers claim their selected pairs are best then others, while some amp manufacturers recommend to use only selected pairs in their amps....that' s crap. I own a 1964 AC30, and when I laid my hands on it some twenty years ago it was beautifully sounding - when I opened it to check the innards I found a lot of components to be out of spec, the biases were uneven, the voltages out of spec, but the sound was fantastic nonetheless.... what I would like to highlight is the absolute nonsense of all this matched/unmatched controversy. Ears and taste should be the judge, if someone wants less or little harmonic distortion then he can put in selected/matched tubes, but he should be aware that his tubes will stay matched only for a few minutes or hours, as the surrounding components' tolerances ( which in the old amps was 10% for resistors and 20% for caps ) will make 'em wear at different rates....
It must be also considered that musicians have different needs and expectations from the ones an audiophile might have.

In other words : Replace that tube without worrying too much about matching...you could even be in for a big surprise, it could even sound better to your ears!

Hope this helps

Regards

Bob

[martin manning]

You guys knew this, right?

http://mixonline.com/news/headline/fender_acquires_groovetubes_0206/

I find that engineers very seldom see eye to eye with "marketeers."

MPM