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AUDIO FORUMS >> Replacement Tubes >> Tube Matching
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Message started by LiquidBlue on 08/08/23 at 03:19:58

Title: Tube Matching
Post by LiquidBlue on 08/08/23 at 03:19:58

I’ve tried to search the forum, but haven’t seen a lot of discussion on this. I’m looking to get some extra tubes for backups and had a question about tube matching. I see a vendor has listed 6N1P-ev tubes that are gain matched and for a bit more has them matched by curves, so matched on multiple points. I’m not sure it’s worth any extra to match these on curves. I can understand there being benefit of matching power tubes, but is there any benefit to matching preamp tubes this way? What about preamp driver tubes vs gain tubes? I’d imagine gain tubes would be more important to be matched/balanced sections, but is there any importance with closely matching preamp driver tubes?

I’d think matching by transconductance or gain and testing for noise and shorts should suffice. What do you all think about the importance of tube matching and methods of matching?

Title: Re: Tube Matching
Post by CAJames on 08/08/23 at 15:43:46

Tube matching is a bit of a hobby horse for me. I'll save my rant for the end, so you can skip it if you want, but as a practical matter I think in most cases "tube matching" is way over rated. I've had tube amps (and a tube tester) for a long time and in my experience tubes need to be pretty far out of alignment for there to be an audible impact. This is esp. true if you have e.g. a UFO25 with which you can adjust the volume for both channels separately, effectively a balance control. For power tubes in push-pull amps matching matters more, for most single ended applications it doesn't matter enough for me to pay extra for it. I would rather buy more cheaper tubes and check them by ear rather than pay extra for "matching" whatever that means.

Now my rant, that I've posted elsewhere. The thing with most tube testers is they are designed to tell if tubes are bad, not if they are "good" or "matched." This means the engineers needed to pick one operating point out of the entire phase space of possible currents and voltages to do a single measurement to determine if a tube needs to be replaced. This is a nearly impossible task, but by and large the tube testers do a really good job solving that problem. The thing is this operating point is likely no where near the operating point where the tubes are used in your amp. So tubes that "match" on your tube tester can be totally different in the amp, or vice versa. And all that assumes your tube tester is even calibrated, which is a whole 'nother thing.

There are more sophisticated tube testers that can test tubes at multiple points i.e. curves, and/or arbitrary points. Decware has one of these so Steve can test tubes at the operating point used in the amp. These do a much better job of actually matching tubes (assuming the curve is close to the operating point of the amp, which is always a question), but as Steve has pointed out even that isn't really enough. What he does is test tubes in an amp to not only match gain, but also harmonics. If you care about matching, that is IMO what it takes to have matched tubes.

I've had a tube tester for a long time, and at first I would totally geek out about matching tubes. But the more tubes I tested the less I found any correlation between test results and sound quality. I still test the tubes I buy, to confirm there are no actual problems and I'm getting what I paid for, and still note the Gm, because why not, but the only test that really matters to me is how they sound. JMO/FWIW/YMMV and all that.

End of rant, we can now return to our regular programming.

Title: Re: Tube Matching
Post by riknbkr330 on 08/08/23 at 21:37:57

Well put CAJames.

My own feeling is that we have a variable in our flaps that are attached to our head. They will change in sound every day due to temperature, amount of rest, whether that's sleep or between listening sessions. And they degrade over time.

I figure tubes do the same thing, whether they are matched or not...and I don't think ears are perfectly matched, especially those of us advancing in age.

I figure if the tubes and the ears are sympathizing on a given day, then enjoy the moment.

If they're not, well shut the damn thing off and go do something else.

Title: Re: Tube Matching
Post by LiquidBlue on 08/09/23 at 06:37:46

Thanks CAJames. Appreciate the insight. I agree, having dual volume controls is very useful. Guess I just was considering what a good baseline is for buying new power and preamp tubes. I get that pairs will drift at different rates, so won’t match for the lifespan of the set, but I also felt that perhaps if they were well matched/balanced to start they may typically have a better chance of sounding better to start. I always considered, especially with power tubes, that tubes that are rated for a lifespan of say 5000 or 10,000 hours will not actually sound at their best for that entire time, as they will degrade differently. So if they are closely matched to start they will at least start off sounding at their best and perhaps if matched very closely, like by matching curves, may sound good for longer. Maybe I’m off in that thinking. Sounds like you have not found a great correlation with strong testing and great sounding. Also good to know matching power tubes is more an issue with PP and not as much a consideration with SET amps.

I don’t have a tube tester, so am buying tubes on the word of the seller. I usually try to seek out reputable sellers and have been happy with most I’ve purchased from in the past, like Brent Jesse, ValvesNMore and have gotten some good tubes from TubeWorld Express. I also have some Cryotones that I’m starting to roll in to try out. My UFO25 is now about 2 months old, so I’m exploring some different tubes for it. The tubes I’ve gotten from Steve have sounded excellent. I’ve noticed he is often out of power tubes for the Zen amps (and I get that he needs to have good stock for new amps being shipped out), so I was looking at some options in Eastern Europe that seem to have good reputation. I’ve purchased a few that way and they have worked out really well, so was going to order a small stash to have some backups. Just want to try to purchase the best quality to start and not waste a lot of time and money buying junk.

Title: Re: Tube Matching
Post by Tony on 08/09/23 at 16:35:50

My UFO25 is about 2 months old, so I’m exploring some different tubes for it. The tubes I’ve gotten from Steve have sounded excellent.

Hi Liquid Blue. I've also had my UFO25 briefly and recently received a remarkable tube, so I wanted to share that with you. The tube is Telefunken PCC88 / 7DJ8 in the Input position.

It was one of those times when just a single tube change made me stop and take notice.

Title: Re: Tube Matching
Post by LiquidBlue on 08/09/23 at 23:24:56

Hi Tony. Thank for the recommendation! I’ll have to check them out. I recently tried out a new tube that I really like as well. I’ve been using the US white label Amperex 7308 and 6922 tubes in my preamp and now in the UFO25 and they’ve been my favorites, but I recently got a Philips MiniWatt PCC88 tube, that sounds great. It brought on some magic. Really clear and detailed top end, with amazing soundstage depth and instrument separation.