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When matching el84's what is the most important measurement to match? The plate voltage, the plate current, or the Gm?

Thanks,
Jon

Matching EL84s (or any other power tubes) is a complete waste of time and money with guitar amps. Power tubes that are slightly out from each other will produce warmer tones, due to the increased presence of even order harmonics. The great famous amps of the past who's sounds we try to copy, all used non-matched tubes.

I've talked to old timers who used to work for those companies, and they say they just had boxes of power tubes and they pulled the next pair or quad out of the box and plugged them into the next amp. I've also A/B tested a pair of closely matched tubes vs a random pair from the same batch, and the tone of the closely matched pair was noticeably sterile compared to the non-matched pair. It seems that Aspen Pitman popularised the idea of using close-matched tubes in guitar amps, presumably because he could make more money that way.

In hi-fi amps OTOH close matching of power tubes, PI tubes and other components, is highly recommended.

In the 60's matching pairs/quads of tubes in audio equipment, which includes guitar and accordion amps, wasn't even discussed among builders and repairmen (they weren't called "techs" at that time; technicians were another stratum entirely). Tube matching was done for certain lab instruments for good reasons and for stereo systems in Beverly Hills houses for ego reasons. Even expensive systems were sold with randomly chosen tubes installed. As long as it sounded good in testing it was boxed and shipped. Repairmen would change both tubes of a P-P pair only if both were bad. No matching, simply pull the next tube or two out of the box on the shelf. The kind of cork sniffing we do today would have been laughable back then, yet we pursue their sound by doing everything they didn't do. Go figure. (I learned electronics in the 60's which were my teenage years and outside of music I didn't participate in the flower people's activities so I do remember).

Z_P's point about even order harmonics is one that would be well taken by all here. Use your ears, people!

KennyO

Ok but what if you have a bunch of used tubes? Does it make no difference if One tube has 20 hours of use and the other has 500 hours?

This was true back in the 50,60's when tubes were manufactured well and the quality control was better. Most likely the variation in tubes were not that great. Today's production and quality is a total different story. I would get matched sets and ideally would check them myself. Don't worry about a 5-10 mA difference but to be way off will effect things. I have quite a bit of old glass and most of the time I can throw anything in a cathode biased amp without worries but occasionally I get a pair that are too far mismatched. It does happen.

To me it appears that modern production tubes have improved a lot in quality. I do quite a lot of amp building for commercial customers, and don't use any matched tubes in them. Same goes for all amps built by the company I often collaborate with. They work fine, are very noise-free, and the customers rave about their tone, which I'm sure the extra warmth produced by non-matched tubes is in important ingredient of. The power tubes used are from modern production sources with an established good rep, and I've not seen any problems with this approach.

Ok but what if you have a bunch of used tubes? Does it make no difference if One tube has 20 hours of use and the other has 500 hours?

As long as they're roughly somewhere in the ballpark. You don't want them so way out that you lose hum cancellation, or one of the pair starts to red-plate. One trick I've sometimes used to "semi-match" tubes, is to run a pair in an amp and swap one of them with a few different ones to get least hum. HTH

Ok, but if you are looking looking to get them in the same "ballpark", what do I look at to determine if they are in the same ballpark?

Plate current, Idle current, Micromhos?

Your ears - that's all. The other stuff can be both misleading, and give you an amp that sounds sterile by comparison. Just pick pairs of tubes that sound great in your amp. Anything else is baloney.

To me it appears that modern production tubes have improved a lot in quality.

They work fine, are very noise-free, and the customers rave about their tone, which I'm sure the extra warmth produced by non-matched tubes is in important ingredient of.

Maybe if production quality gets too good we will be paying a premium to get an unmatched set.

Maybe if production quality gets too good we will be paying a premium to get an unmatched set.

I can see the cork sniffers starting something with this. " Well I find in a M*** amp that when I use tubes about 6 ma off I get the best tone." Then come the flood of requests to various tube sellers for tubes 6ma apart.
Lord have mercy!!!

The matching thing is bad enough. And GT could come up with a system for colour coding the level of unmatching to make it 'simple'.

I have a bunch of old pulls of both el84 and 6v6's. There is not a match in the whole lot of them, meaning different brands, types, black plate, smoke glass etc. Is it ok to mix and match that way too?

You're less likely to find a pair that will work together, but it is possible. Basically you will need to try out various pairs and chose for least hum, also checking in a dark room for any red-plating.

As a further check you can measure the anode (plate) voltage of each tube, which should be roughly within a few volts of each other. If you have a known good or matched pair you can take the anode voltage readings to use as a baseline for comparison with other pairs of tubes. There will always be a few volts difference due to the two sides of the OT primary having slightly different DC resistances.

Also be aware that sometimes tubes labelled with different brand names can be the same inside. I've had a 1970s NOS Brimar 6V6 and a Sovtek which ran together perfectly with only a few mA difference. It turns out that both were actually re-labelled Russian 6pi6 tubes.

Your ears - that's all. The other stuff can be both misleading, and give you an amp that sounds sterile by comparison. Just pick pairs of tubes that sound great in your amp. Anything else is baloney.

This may be the greatest truth I have ever seen on the Web.

Well, the aim of building tube amps is to get something that sounds great to our ears. So let's pick tube pairs that make our amps sound the best.

This new thread is a great example of how you not only don't need the tubes to be matched, you can even use completely different kinds of tubes in a push-pull pair - http://www.18watt.com/modules.php?name= ... ic&t=23669

I wonder if you could wire in a 10 or 25 ohm pot between one of the EL84 cathodes and the bias resistor and then dial in a little "unmatching". Then tweak it by ear to taste.

The hum is the only real problem - a badly matched pair will hummmm ...

There are some designs that have balance pots to minimise the hum.

Your ears - that's all. The other stuff can be both misleading, and give you an amp that sounds sterile by comparison. Just pick pairs of tubes that sound great in your amp. Anything else is baloney.

AMEN to that!

OK, Let’s take a step back here and think a bit;

Even if you had a pair of super duper matched tubes within .0001 of a mA, when you’ll play your amp, tubes will not wear out at the same rate so what’s going to happen after a couple of gigs? Your tubes will be…unmatched!
Is your amp going to have a melt down? Nope! Is you amp going to start doing nuclear fission and cause a nuclear holocaust? Probably not. Are the tubes Gods going to come down and haunt you? Well.., if you buy into the tube matching voodoo, then they probably will!

Hey, I remember as a teenage bringing a Dual Showman to a party to find out that one of the tubes had fell at the bottom of the cabinet and broke. What did we do? We went to the local music store, bought a 6L6, popped it in and partied on, all that without biasing! Heck, I’d never even heard of biasing back then!!

Like Zaphod_Phil said, use your ears and forget about that Groove Tubes (and others) tube matching hype.


Ok, rant’s over.. thanks for listening!

I've been slowly building up a small NOS stash, and just purchased a pair of 6P14P-K tubes, match is 10 ma apart.....I appreciate the contributors to this thread, the match was a concern, though not red plating.......it does sound good......and will probably sound better when I change the cathode resister in the amp...... running a little cold......

How far apart is too far on the match?
I gather when there's a hum problem it's too far......but at what point in a mismatch does that tend to be?........
Much respect, and thanks in advance...........

New here!! 1st Post - Guitarist / indie audio engineer - just checking if I install two Telefunken EL84's Power Tubes from Germany NOS - non matched pair - testing "strong" - that my new VOX AC10 C1 amp will be OK. I like the Telefunken sound - bright Beatles'/rock. Concerned about voiding warranty.

Hard to see "red-plating" as amp has a closed back. I like the idea of working with even-ordered harmonics to get a great rock / blues sound. "Hum" will be the test if anything is wrong.

Right now, new amp is very quite: Sweetwater installed JJ's in both Preamp (2) / Power Tubes (2). If / when I hear noise, it goes away depending on 1) how close I am to the amp and 2) the direction my guitar faces the amp. Four feet away from amp = no noise. Some noise when gain is turned up past 1pm.

Apartment studio. VOX AC10 C1 = Gain 9:00 and MV anywhere from 11:00 to Max. EQ = Bass rolled off to 9:00 (gets rid of boomy sound with E Chord), Treble @ Noon, with Reverb Off. With these settings, I get a clean sound that works well with fuzz pedals. Putting amp on a Gator stand further reduces a boomy low end sound.

Today, will be installing Telefunken ECC83 NOS tubes (2) into the Vox AC10 C1 preamp section: recently discovered a batch of tubes and a Precision Tube Tester hidden in a corner behind a Ludwig bass drum. Cleaning the studio has rewards! Want to see if sound gets better from what JJ' Tubes can do.

New to Strat guitars / Vox amps. For years, played a Tele / EMG 85s with a Fender 1966 Blackface Champ (Telefunken ECC83) modded by Gerald Weber (Studio Rec/Stage gigging - mic'd) - Texas Tone (on/off) Raw vs EQ sound, Feedback (on/off), and a larger "Texas sized" OT.