[JTbbb]

Tube testers are a bit of a hobby horse for me, so those who have heard this rant before will need to excuse me.

<rant>The thing about (most) tube testers is they are designed to test if tubes are bad, not if they are good or matched. The engineers at Hickok, HP and etc. had an almost impossible job: to pick a single operating point from the entire phase space of currents and voltages to test to determine if a tube needs to be replaced. And by in large they did an amazing job solving that problem, but IMO, the relevance to audio is limited. Yes, if you pay for a "NOS" tube and it tests weak there is a problem. And I always test tubes (and adapters) for shorts before putting them in an amp. But in general the more tubes I test the less correlation I find between test results and audio quality. Weak tubes can sound great, and last a long time in an audio application. Or put another way, your amp and your ears is really the best way to test tubes for audio.

And then there is "matching," which is a whole 'nother kettle of fish. Is the operating point you test the tubes at the same as the operating point in your amp? Probably not, so just because tubes match on your tester doesn't mean they are matched, and visa versa. There are fancy testers that can test tubes at an arbitrary operating point, or even better over a range of operating points (curve tracers), and those are truly useful tests. But they are even more expensive than a "plain" Gm tester. Some tube dealers will include the curves with tubes you buy, and you can buy a lot legitimately tested and matched tubes for what a high end tester costs these days. </rant>

All that said, if you're really interested in tubes, a tester is a useful (and fun) thing to have, and as far as hobbies go it is way better than cooking meth, as a tell my wife.

I have posted this extract from a professional tube tester in this Forum before, and is worth posting again, as it ties in nicely with some of your observations. This relates specifically to 5998’s / 421a’s.

“The PC/TC figures are pretty much a standard that people use to buy / sell valves to give an idea of their ‘goodness’, but in reality the 421A / 5998s are very high power triodes used mainly in Military applications back in the day, so to be honest for the purposes of matching the valves for your preamp, the PC score is really irrelevant, whether a valve can drive 90mA or 40mA is of no consequence when it is in circuit driving 5/6mA, they will pretty much all work until they become noisy or completely exhausted. A more useful parameter to match against is the TC (transconductance, loosely described as the gain of the valve), so use that as a basis for matching, but again don’t worry unduly, because I think you would be hard pushed to hear the difference between a valve with a TC of 9 or 14, but always good practice to get as close as possible. The main criteria with your amp I would suggest is how noisy they are, as that directly affects the listening experience, old valves can become noisy and microphonic, as you know.”

 

[triod750]

I read somewhere that every time you test a tube you shorten the life of it with no real benefit from the test result (for most people). There was a long technical explanation that went over my head and disappeared without trace. Also, the tubes need to become really warm to show their true values and they are rarely tested that way.
I have a short bottle Sylvania 6SN7W that tests NOS and is very noisy. I'm open for high bids.

 

[leftside]

I have posted this extract from a professional tube tester in this Forum before, and is worth posting again, as it ties in nicely with some of your observations. This relates specifically to 5998’s / 421a’s.

“The PC/TC figures are pretty much a standard that people use to buy / sell valves to give an idea of their ‘goodness’, but in reality the 421A / 5998s are very high power triodes used mainly in Military applications back in the day, so to be honest for the purposes of matching the valves for your preamp, the PC score is really irrelevant, whether a valve can drive 90mA or 40mA is of no consequence when it is in circuit driving 5/6mA, they will pretty much all work until they become noisy or completely exhausted. A more useful parameter to match against is the TC (transconductance, loosely described as the gain of the valve), so use that as a basis for matching, but again don’t worry unduly, because I think you would be hard pushed to hear the difference between a valve with a TC of 9 or 14, but always good practice to get as close as possible. The main criteria with your amp I would suggest is how noisy they are, as that directly affects the listening experience, old valves can become noisy and microphonic, as you know.”

Good post and VMT:

whether a valve can drive 90mA or 40mA is of no consequence when it is in circuit driving 5/6mA, they will pretty much all work until they become noisy or completely exhausted. A more useful parameter to match against is the TC (transconductance, loosely described as the gain of the valve)

My tubes testers have more than paid for themselves now. Quite a few tubes I've received were 20% less strong (20% less TC/Gm) than advertised. Tested on both my tube testers. I either received a hefty discount (especially if advertised as NOS) or simply returned the tubes.

If you're a techy, and like to know all the parameters of your tubes, then the modern digital tube testers that you can hook up to your PC are also very interesting.

 

[leftside]

I read somewhere that every time you test a tube you shorten the life of it with no real benefit from the test result (for most people). There was a long technical explanation that went over my head and disappeared without trace. Also, the tubes need to become really warm to show their true values and they are rarely tested that way.
I have a short bottle Sylvania 6SN7W that tests NOS and is very noisy. I'm open for high bids.

Most tube testers will warm up the tube for a minute or so before testing. The tube won't get much "warmer" after this period. Of course every time you use a tube or test it, you shorten the life span of it. But this decreased life span is minimal. And how often do you test a tube? Once when purchased. Maybe again if you are noticing any issues, or have been using for a few years. And maybe again if you sell it. Personally, I like the added security of knowing what is going into my tube equipment has at least tested well.

Once you get a decent tube tester, your perspective changes and you can't go back

 

[bcowen]

Tube testers are a bit of a hobby horse for me, so those who have heard this rant before will need to excuse me.

<rant>The thing about (most) tube testers is they are designed to test if tubes are bad, not if they are good or matched. The engineers at Hickok, HP and etc. had an almost impossible job: to pick a single operating point from the entire phase space of currents and voltages to test to determine if a tube needs to be replaced. And by in large they did an amazing job solving that problem, but IMO, the relevance to audio is limited. Yes, if you pay for a "NOS" tube and it tests weak there is a problem. And I always test tubes (and adapters) for shorts before putting them in an amp. But in general the more tubes I test the less correlation I find between test results and audio quality. Weak tubes can sound great, and last a long time in an audio application. Or put another way, your amp and your ears is really the best way to test tubes for audio.

And then there is "matching," which is a whole 'nother kettle of fish. Is the operating point you test the tubes at the same as the operating point in your amp? Probably not, so just because tubes match on your tester doesn't mean they are matched, and visa versa. There are fancy testers that can test tubes at an arbitrary operating point, or even better over a range of operating points (curve tracers), and those are truly useful tests. But they are even more expensive than a "plain" Gm tester. Some tube dealers will include the curves with tubes you buy, and you can buy a lot legitimately tested and matched tubes for what a high end tester costs these days. </rant>

All that said, if you're really interested in tubes, a tester is a useful (and fun) thing to have, and as far as hobbies go it is way better than cooking meth, as a tell my wife.

Very valid points and spot on from my experience. One rant to add: if you buy a vintage tester on Ebay or wherever, unless that tester has already been refurbished and calibrated by someone else (of perhaps unknown qualification and knowledge), at a bare minimum the electrolytic caps will need replaced. 50+ years is way beyond the service life of even modern electrolytics, and it's practically a guarantee that most of the caps will be significantly out of spec (if not dead altogether) in a vintage tester. In most of the testers it's not a difficult job, but you'll have to calibrate it afterwards and the process for that is usually not contained in the standard O&M manual. If you buy a model that was fairly popular in the day there is good info available now from several different websites, but always best to check for documentation before buying a tester you can't get calibration information for. If you don't replace (again, at minimum) the capacitors and calibrate it, whatever readings you get are worthless.

Like you I've enjoyed messing around with them as a hobby in and of itself, but understanding their limitations at the same time. The bulk of the vintage testers were portable units designed for a service person to take with them to the house of Joe Customer to fix their TV or radio, and to quickly determine whether a tube was good or bad. They were not designed or intended as laboratory-grade measurement instruments. All that said, I think they do provide value in testing for shorts and high interelement leakage, and even the less expensive emission-only testers do a good job in that area. As well, I find value in testing dual triode signal tubes. Even though the tester is (likely) applying a different plate voltage to the tube than the component it'll be used in, the relative reading between the triodes provides some good info -- If one triode is 30% different than the other at 150v (my Hickok), it'll likely be around a 30% difference at some other voltage too. But if someone is looking for a tester that can provide comprehensive data and has the capability to provide voltages that mimic the component the tube will be used in, then a modern tester or curve tracer is the only way to go. Just prepare your wallet.

 

[leftside]

And thanks to @bcowen for his advice on tube testers to me a few years ago. In the end, I had to prepare my wallet... but after what I had learnt, I knew I'd be going that direction in the long term anyway.

 

[shwnwllms]

I couldn't say whether the metal cans compare to the 6S5S. Maybe one day you hoarders will let some of them go!

(But seriously, I blinked one day and all the 6S5S were gone. What happened?)

You gotta be quick. I just scored another pair

 

[bcowen]

And thanks to @bcowen for his advice on tube testers to me a few years ago. In the end, I had to prepare my wallet... but after what I had learnt, I knew I'd be going that direction in the long term anyway.

Thanks for the thanks! But you left me in the dust pretty quickly. Now I need to come to you if I need a tube seriously tested.

 

[triod750]

Once you get a decent tube tester, your perspective changes and you can't go back

This could also be a good reason not to get one ...

 

[raindownthunda]

This could also be a good reason not to get one ...

Ignorance is bliss (someone had to say it)

 

[Designsfx]

You gotta be quick. I just scored another pair

I’ve never used the 6S5S tube- is someone able to put words to the magic?

 

[nwavesailor]

You gotta be quick. I just scored another pair

Damn, you are goin all @Wes S here in your quick draw!

 

[steve468]

You gotta be quick. I just scored another pair

AAAAAHHHHHRRGGH!

 

[shwnwllms]

These 1943 Hytron 6C5’s are sounding mighty fine

 

[g0ldl10n]

These 1943 Hytron 6C5’s are sounding mighty fine

Appears I have the exact same tubes as you, same numbers and all - they've been in my collection for a good part of a year now, and I agree, I think they sound wonderful - btw, how did you date them?