[Mr Trev]

It really depends on the seller. Some state that a 20% spread is a "great match" and I don't agree with that at all. I think more of a general but unwritten industry convention is that 10% or less difference is a good match. I try for 5% with the tubes I use. But a lot depends on how high they test. If both sections are within 20% of NOS, any imbalance will likely be inaudible (for instance, one section tests at 10% higher than bogey/NOS and the other tests at 10% below bogey/NOS). In your example, if 2200 is bogey, then the other section is still above minimum (with minimum usually being around 60% of NOS), so an imbalance probably won't be audible....probably. Depends on the tube and the amp it's used in as well. Power tubes like 6550's, KT-88's, EL-34's, etc are going to be less forgiving with big GM or emission differences. Small octals and novals not so much...usually. But 1600/2200 is a 22% difference. Not a tube I'd go after personally with that big a difference, but that's just me.

Don't know if this explanation helps at all or just confuses things worse (which is one of my specialties ).

That covered it. What measurements mean are one thing I've never really bothered looking into - I'm getting too old to do new book learning, it'll end up pushing out the stuff I've already learnt.

So, how do test values effect the sq?
Back when I first bought a tube amp and was wondering why anybody would even look at ads where the tubes have lousy test values. Then I started thinking… well, what if I went out and bought a whole bunch of "bad" tubes for dirt cheap. Then listen to 'em and see what I like so I'd know what "good" tubes to start looking for. The sticking point was I have no idea how bad a measurement can get before the sound falls off a cliff.

 

[Ripper2860]

Unbalanced triodes tend to manifest itself as channel imbalance. Most amps auto-bias to try and make-up for element imbalance, but there's only so much auto-biasing can do. Where that line is, I'm not sure, but 10% seems a reasonable number where one is not at the mercy of corrective measures in the amp.

 

[bcowen]

That covered it. What measurements mean are one thing I've never really bothered looking into - I'm getting too old to do new book learning, it'll end up pushing out the stuff I've already learnt.

So, how do test values effect the sq?
Back when I first bought a tube amp and was wondering why anybody would even look at ads where the tubes have lousy test values. Then I started thinking… well, what if I went out and bought a whole bunch of "bad" tubes for dirt cheap. Then listen to 'em and see what I like so I'd know what "good" tubes to start looking for. The sticking point was I have no idea how bad a measurement can get before the sound falls off a cliff.

Here's the chicken/egg, cart/horse thing: if you get a tube and it doesn't sound good to you, is it because the tube doesn't mate well with your equipment or preferences, or because the tube is worn out and not producing sound like it should? That's the whole reason I got a tube tester (or 2....hundred), as I've purchased many tubes over the years that were well spoken of by many, and when I listened to them I thought they sounded like dreck. Once able to test some of those I found they were well below minimum GM levels, so it wasn't that the tube (type) itself didn't have the qualities many spoke favorably of, it's just they were worn out. There are some good Ebay sellers that are honest and reliable, but unfortunately they are outnumbered by either sheer fraudsters or people that aren't necessarily dishonest, they just don't have a clue.

 

[jonathan c]

Here's the chicken/egg, cart/horse thing: if you get a tube and it doesn't sound good to you, is it because the tube doesn't mate well with your equipment or preferences, or because the tube is worn out and not producing sound like it should? That's the whole reason I got a tube tester (or 2....hundred), as I've purchased many tubes over the years that were well spoken of by many, and when I listened to them I thought they sounded like dreck. Once able to test some of those I found they were well below minimum GM levels, so it wasn't that the tube (type) itself didn't have the qualities many spoke favorably of, it's just they were worn out. There are some good Ebay sellers that are honest and reliable, but unfortunately they are outnumbered by either sheer fraudsters or people that aren't necessarily dishonest, they just don't have a clue.

...about tubes, tube testing, and test result presentation.

 

[Hyde00]

Yup, they don't seems to be very common anymore.
There's this one: https://www.etsy.com/ca/listing/938971066/ei-yugoslavia-12au7-ecc82-vacuum-tube
I'm not sure what vintage mine is, but it's branded "Orion Radio" (from Hungary, I think).

The one question I'd have is that the "Transconductance measured 1600/2200 micromhos". Apparently 2200 is typical for "new". But how far off between the two sides is too much? - this would be a general question for all tubes (@bcowen maybe you can answer this for me since I really don't know what any of these measurements actually mean).

Otherwise, Jeffrey at Lowtechelec is a great guy to deal with, and his prices are extremely reasonable for us up north.

lol damn I never knew etsy sells tube too, good find! Though based on what bcowen said maybe I'll stick to Matshushita and RCA Clear Top this time to be on the safe side.

Thanks for the explanation though!

 

[Ripper2860]

That seller is very reputable and recommended by several at HF - myself included.

 

[bcowen]

That seller is very reputable and recommended by several at HF - myself included.

And @Ripper2860 has a thoroughly rebuilt and pristinely calibrated tube tester so he can check what he gets to be sure it's as advertised.

Here's my current project. Let's just say it will look a wee bit better when I'm done with it (oh, and will work too).

 

[jonathan c]

And @Ripper2860 has a thoroughly rebuilt and pristinely calibrated tube tester so he can check what he gets to be sure it's as advertised.

Here's my current project. Let's just say it will look a wee bit better when I'm done with it (oh, and will work too).

Oh, I’m sorry: I thought that this project was done.

 

[bcowen]

Oh, I’m sorry: I thought that this project was done.

This is my third Hickok 800A. Honestly, those pics may be from the last one I did, but the current one looked pretty much the same. And it is almost done...

 

[Mr Trev]

Here's the chicken/egg, cart/horse thing: if you get a tube and it doesn't sound good to you, is it because the tube doesn't mate well with your equipment or preferences, or because the tube is worn out and not producing sound like it should? That's the whole reason I got a tube tester (or 2....hundred), as I've purchased many tubes over the years that were well spoken of by many, and when I listened to them I thought they sounded like dreck. Once able to test some of those I found they were well below minimum GM levels, so it wasn't that the tube (type) itself didn't have the qualities many spoke favorably of, it's just they were worn out. There are some good Ebay sellers that are honest and reliable, but unfortunately they are outnumbered by either sheer fraudsters or people that aren't necessarily dishonest, they just don't have a clue.

Sure, I get that, what I was wondering is how bad a tube can test, but still sound fine. Is min. GM the cutoff?
Hypothetically, could I go out and buy half a dozen known bad testing TSRP (but still sound ok) for dirt cheap. Listen to one for 6 mo. (or until it is unquestionably fubar), toss it, repeat.

 

[Ripper2860]

..."but still sound OK" is pretty subjective. Another's OK sounding tube would likely be 'Batman Bill's' absolute trash sounding tube.

 

[bcowen]

..."but still sound OK" is pretty subjective. Another's OK sounding tube would likely be 'Batman Bill's' absolute trash sounding tube.

Hate to say I agree with you, so I won't. But I do.

I don't know that there's an 'either/or' answer to the question, honestly. Some tubes may sound just fine at minimum and even below, and some may start sounding soft with a loss of dynamics and reduced bass punch and drive. And it could be manufacturer specific as well, for instance an RCA 12AU7 might sound good at 50% GM while a Tung Sol wouldn't (I'm just tossing those out for illustration, not as any known fact or experience with either one).

 

[jonathan c]

Hate to say I agree with you, so I won't. But I do.

Or: “I’m surprised that you agree with me! Well done!”

 

[jonathan c]

Hate to say I agree with you, so I won't. But I do.

I don't know that there's an 'either/or' answer to the question, honestly. Some tubes may sound just fine at minimum and even below, and some may start sounding soft with a loss of dynamics and reduced bass punch and drive. And it could be manufacturer specific as well, for instance an RCA 12AU7 might sound good at 50% GM while a Tung Sol wouldn't (I'm just tossing those out for illustration, not as any known fact or experience with either one).

Also, wouldn’t such parametres as current draw / current required from a tube within a circuit affect sonics of a tube <= minimum: ie, “how hard a tube has to work” [ non-EE ruminating here] ?

 

[bl4scott]

I have been running 6sn7 primarily since I got my vali 2 but intrigued by the 12au7. Is it worth getting an adapter and venturing down this rabbit hole as well?