Preamp tube tester

Scooby9261

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I have a tester for 6L6 type tubes. But im looking for a relatively cheap priced tube tester that tests preamp tubes. Curious what you all would suggest.
 

corliss1

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But really, the best answer to "how do I test a tube" is "use it in the application you want and see if it performs well"

For example, something with some noise could be just fine in a trem oscillator, but not be suitable for V1. A tester won't tell you that. A tester also won't show you microphonics, or use any considerable voltages.

A tester can tell you if a tube is bad - it can't tell you if a tube is good.
 

dan40

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I have a tester for 6L6 type tubes. But im looking for a relatively cheap priced tube tester that tests preamp tubes. Curious what you all would suggest.


What do you need the tester to test for? Are you looking for actual transconductance readings or just a simple shorts and emission reading? Orange Amplifiers use to make a small tube tester that was fairly affordable but unfortunately they stopped selling them. You can still find them used though. Other than that, your choices are limited to high dollar Amplitrex units or old vintage testers found on Ebay. The older ones found on Ebay will need a reconditioning and calibration to give you accurate transconductance readings but you may find some older units that will provide a simple shorts and emission test. None of these units will tell you if a tube is noisy though. As Corliss1 mentioned above, an actual amplifier is often the best tester when it comes to preamp tubes.
 

Mowgli

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There are different types of tube testers but the better ones are expensive.

One way, in my opinion, to look at “preamp” tubes like 12ax7s, in general, is to recognize that most are relatively inexpensive and tend to last a long time. So buy a few spare ones from a reputable dealer and use them for “comparison testing” — assuming they are new good strong tubes free of abnormal noise. If you don’t have a lot of tubes or a lot of amps the cost of a tube tester may not be worth it.

An important utility of a tube tester is to 1st make sure that the tube doesn’t have any shorts which could possibly damage the amp.

The other utility is to test for strength of the tube as an indicator for longevity.

Some will correctly assert that shorts are rare so, statistically, the odds are strongly in your favor that your tube doesn’t have a short. If you feel that the odds are in your favor, not testing for shorts is a risk you may wish to take.

After shorts have been ruled out or the risk for shorts are disregarded, then the next big test is functional; how do they sound?

With a tube tester, a tube may test “strong” or “good” but be noisy or sound less than desirable when it is in your amp! So a tube testing “good” isn’t the final word.

Realize that substituting the tube in question for a known good tube should answer most questions about the tube’s function and desirability with regard to tone. But it won’t project the tube’s longevity. Again, only a tube tester can give you an idea about that!

So, without a tube tester, you really have no idea if that newly acquired preamp tube has shorts or if it should last as long as expected.

I say that if it sounds good, go with it until it sounds bad. Having several “known” good-sounding spare preamp tubes and using them as substitutes may save you the cost of a tube tester.

But if you need to know about both shorts and expectations about tube longevity you need access to a tube tester.

My 2 pennies.
 

Wally

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Funny enough, I picked up an emission tester a couple weeks ago, and it just tells me every tube is good, even known-bad ones :)

“even known bad ones”…. What were the problems that established these ‘known bad tubes’ as being ‘bad’.
An emissions tester will indicate a short, and that is a bad tube. If your tester shows a known shorted tube as good, your tester is not functioning properly. An emissions tester can indicate a tube with ‘weak life’. I have seen such tubes that would not function in a certain circuit but would function in another. Interesting, right? An emissions tester can indicate a bad grid.
IF your tester shows tubes that are known to have shorts, extremely weak emissions, or a bad grid to be ‘good’ tubes, your tester is not functioning properly.
An emissions tester is good for finding shorts, indicating a bad grid, and for indicating weak life. Other than that, it cannot ascertain anything else about a tube. Many things make a tube a ‘bad’ tube…and certain ‘bad’ tubes can still pass signal.
One thing about using an emissions tester. Harm can be done to the tube if it Is subjected to long tests in the emissions mode. I keep a tube in the emissions test mode for only the few seconds it takes to see the test.
 

doof

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“even known bad ones”…. What were the problems that established these ‘known bad tubes’ as being ‘bad’.
Excess noise, crackles, etc... that follow the tube. Thanks for taking the time to write all that out! After my post yesterday I did a deeper dive into emission testers vs transconductance testers and spent an hour or so reading what you summarized so well. So I suppose a better choice of words would have been 'known-bad-in-a-particular-circuit'.
 

bparnell57

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Excess noise, crackles, etc... that follow the tube. Thanks for taking the time to write all that out! After my post yesterday I did a deeper dive into emission testers vs transconductance testers and spent an hour or so reading what you summarized so well. So I suppose a better choice of words would have been 'known-bad-in-a-particular-circuit'.
A lot of times those "noisy" tubes are great for tremolo circuit use. No need to discard them most times.
 

schmee

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Yes, it's often the noise; hiss, crackle etc that vintage tubes fail at. I have a ton of old AX7's that test great but are too noisy to use. One problem is guitar amps seem to be higher gain devices than say Stereo amps. Some of these noisy tubes are fine in Stereo applications.
A little BK Dyna jet tube tester works pretty well for general testing and are not too expensive. 666, 707 etc models.
One thing I have discovered and have never figured out is that some modern 12AX7 tubes will not test! Many read bad. No life, ZERO on the meter. Brand new ones! Yet are fine in amps. I thought it was my tester, but I pulled out my other tester and ditto. I dont know if I just happen to have two bad testers or ...? But if I stick a vintage 12AX7 in they test!
 

bebopbrain

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Use an amp, maybe a junked amp. Maybe an amp like the 5F6A where V1 is the first stage of two separate input channels. You will need a voltmeter.

Apply a DC voltage to the input jack (let's say, 0VDC to start). Measure the cathode, grid, plate, and supply voltages. Now you know the all voltages and currents for the triode. Apply 0.5VDC and try again. Apply -0.5VDC. Keep going.

You will know everything there is to know.
 

RetiredUnit1

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I have a TC162 which is a solid state tube tester. Nothing but good words about it and it was fairly inexpensive. The picture isn't mine, but they look the same.... The thing I like is you can buy a calibration module for it and calibrate it in a few minutes....
1657398205915.png
 




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