Tube tester

[B-string]

Note: Unless the tube has a short or no emissions try them before you toss them. Tube testers are no where near 100%. Even tubes that test "good" in a tester can be very bad in audio use but work fine in different circuits.

 

[Jerrold Tiers]

+ several for the idea that the usage circuit is the best tester......

Not always practical, but........... testers vary a ton in what they test..... the best tester allows you to vary everything.... that's the type the engineers back at the tube makers used.... I visited Richardson Electronics once (a tube vendor back then), they had several of those, several more production test setups, and a number of automated production lines.

meters out the wazoo...... What we were doing up there was working with them on a test for microphonics.... one that resulted in a number, not a noise.....

So, longwinded way to second the idea of you making up your own tester.... You don't need to test every kind, you only need to test a dozen or two types at most, and you know what they are... you can look up their specs, and can make a tester to give you any spec you want, quantified by an actual number.

You will learn enough that you might end up as the regional "tube guru" ......... there are worse ways of starting in business.....

 

[two fingers]

Thanks Jerrold and B string. One of my instructors is an old tube head. Maybe I can get with him about making one. That WOULD be a fun project and probably a huge learning experience.

 

[Lo-E]

Here's a very good read on tube testers: Invalid Link Removed

I was going to post this link, but NashvilleBill beat me to it. It's about the best treatise on the topic I've read.
As someone else here stated, the best test is the circuit in which it will be used.

I use a Heathkit TT1 - a very good transconductance tester that I calibrated myself. I'd like to find a Triplett 3444 one of these days, but I'm in no rush.... I have basses to buy!

In general, the Hickoks, while excellent testers, are usually overpriced. The most important thing is to know your tester well and fully understand what it tests, how it tests it and - most importantly - what it doesn't test.

 

[B-string]

Thanks Jerrold and B string. One of my instructors is an old tube head. Maybe I can get with him about making one. That WOULD be a fun project and probably a huge learning experience.

Include beans-on-toast as well. He brought this up also in post #9. It sounds like the best learning experience you can get and the icing is you get course credit. Old tube head.....I like it. Get that knowledge from him before the vacuum is lost (vacuum tube joke).

 

[two fingers]

OK so I read the whole stinking thing (that guy is a TRIP). Let me ask a question to see if I get it. If the best tube tester is the amp you are going to put it in, what's the "test" part? Once the tube is in place, do you simply use a meter and take measurements at certain points? Do you use the actual pins or what? (If this is something best shown in person, I can get with that instructor sometime nest week. But my curiosity is peaked right now so I thought I would ask.)

Short version. What's the procedure for testing/measuring a tube in the actual socket where it will be doing what it does?

By the way, you guys are great! This is fun and interesting stuff! Thanks!

 

[two fingers]

Include beans-on-toast as well. He brought this up also in post #9. It sounds like the best learning experience you can get and the icing is you get course credit. Old tube head.....I like it. Get that knowledge from him before the vacuum is lost (vacuum tube joke).

Yes sir!

Thanks beans!

 

[B-string]

OK so I read the whole stinking thing (that guy is a TRIP). Let me ask a question to see if I get it. If the best tube tester is the amp you are going to put it in, what's the "test" part? Once the tube is in place, do you simply use a meter and take measurements at certain points? Do you use the actual pins or what? (If this is something best shown in person, I can get with that instructor sometime nest week. But my curiosity is peaked right now so I thought I would ask.)

Short version. What's the procedure for testing/measuring a tube in the actual socket where it will be doing what it does?

By the way, you guys are great! This is fun and interesting stuff! Thanks!

That is were the learnin' part comes in! Mere voltage gain ratio with a meter only tells part of the story. You are affecting a large DC voltage with a non-fixed frequency AC voltage. Oscilloscopes will help clue you into the changes. One of the big falling out with tube "testers" is they take measurements with DC voltage or a fixed frequency AC source. I actually prefer the British name Valve over tube as it more accurately portrays it's function.
Hmm recording plate change under an audio sweep at different amplitudes.....naw the work is yours to have fun with.

 

[beans-on-toast]

Too add to that, what you have to understand is that in order to test a tube, you need a set of conditions under which you can perform tests. It will provide you with a consistent way of testing the tube. In a tube tester, under its set of conditions, you measure a tube like a 12AX7 or a 6L6GC and the manufacturer tells you what sort of plate current and transconductance readings (if it is a good tester) you should see for the tube to be considered good. It will tell you if the tube is a dud. It can tell you if it is microphonic. This gives you some information about how the tube is working. Plug in another 12AX7 tube and you can compare it to the last one. What it doesn't do is tell you how well that tube is going to function or sound in a particular amp. A tube that tests good at 250V on the plates in a tube tester may not test good when plugged into an amp with 550V on the plates. The plate and screen voltage levels in most tube testers are not as high as what you see in many amps. There are exceptions as John pointed out below. The [Invalid or Expired Link Removed] AT1000 can go up to 500V. A lot of factors affect how a tube performs and a tube tester doesn't and can't replicate what is seen in the amp unless it is custom built to do so. You obviously can't build a tester to match the conditions found in every circuit that it is going to be used in. So you makes some compromises and say, I'm going to test my tubes under these conditions only. That's what a tube tester does. There is no standard when it comes to how a tube tester should test a tube. The readings from one tester may not be the same as the readings from another make.

We are saying to test the tube under similar conditions that it will see in the amp. Use the same plate and screen voltages and bias method. Measure the cathode current draw and transconductance under those conditions. Especially do this when matching tubes (see the last paragraph). That will give you a better indication as to how it will perform in the amp. When it is in the amp, listen with your ears! All the readings help you determine if it is going to work. Your ears are going to tell you how well it is working.

When I bias an amp I set it up to ensure that the tube is performing within specifications. Then I adjust it by ear. When it sounds best, I recheck that it is operating within spec. In the end you want it to sound optimal.

When you buy a matched set of tubes, they choose a plate and screen voltage, they choose a bias method. They match the tubes, usually for current flow and transconductance under their set of conditions. Plug them into your amp and they may not be matched. A good seller will ask you what make of amp you have and match them under the conditions that the amp presents. Unfortunately, many sellers do not do this.

 

[johnk_10]

I use a maxi-matcher for output tubes and my Triplett 3444 for preamp and rectifier tubes. AFAIK the triplett and the old heathkits are the only older tube testers that test preamp tubes at high voltages. my Hickok 800A doesn't (but it's still a pretty good one).

once they pass all of the tests in the testers I then put them in the amp for the 'real' test.

 

[seamonkey]

Checking out the Orange it is actually quite brilliant.
It actually runs through a bank of tests, some at high voltage. It then rates the tube.
Simple to use, but a little expensive, but not for a store to own.
I can pretty much see many music stores having one just for people to come in check their tubes, measure how much life is left, match them, and of buy tubes, but only after testing it.
I can see people swapping tubes with other players, trading ratings of tubes just to match.
No why was it drug stores had testers? And what's the first thing a tech does with a tube amp? Orange is brilliant!

 

[B-string]

Where are you finding detailed info? All i can find is marketing blurbs and pics that show a 19VDC input jack. What kind of "high Voltage" from a 19 volt DC power source?

 

[two fingers]

Hmm recording plate change under an audio sweep at different amplitudes.....naw the work is yours to have fun with.

See, that's what I was thinking! I was leaning that way but didn't know how to phrase it. Hmmmmmmm........

Come along Jamerson (my evil monkey). We must go back to the lab. Mwa ha ha ha ha. (cue scary organ music)

 

[B-string]

The nice thing about these days is a laptop will have more than enough processing power and sample rate to handle the operations necessary for a test gig. If that winds up being the only way to chart and compile.

 

[johnk_10]

I suppose that they're using a voltage multiplier to get the high voltages for the orange tester. the only thing I don't care for is that it really doesn't tell you much about the tubes other than giving them a number and pass, fail, good rating, and it doesn't tell you anything about noise or microphonics, but it's probably fine for a music store.

IMO, although it's a lot more expensive then the Orange, I think this one would be more useful:

Invalid Link Removed



to go along with this:

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[beans-on-toast]

The maxipreamp looks like a very nice unit. It would be nice if it had a computer interface to save test results.

 

[Mad Maestro]

Link Removed has links for commerical tube testers and DIY projects.