New tubes testing bad?

Discussion in 'Amps and Cabs' started by Figaro, May 20, 2015.

  1. Figaro

    Figaro Supporting Member

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    I have an old simple tube tester that you set the controls according to the type of tube, push a button and it's meter rates the tube on a scale, basically good or replace. Not a real good tester. But I've noticed that some brand new tubes that I've used and tested show that they should be replaced! They still work and sound ok but the tester says they should be replaced!

    I'm just wondering if others with a tube tester have found brand new tubes that work, but test bad?

    Yes Blue Strat, this means you!
     
  2. Heady Jam Fan

    Heady Jam Fan Member

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    I'll bet your tester is not calibrated.
     
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  3. Figaro

    Figaro Supporting Member

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    I knew that comment was coming. No, it hasn't been calibrated. But I'm comparing the same kind of tubes at the same settings and the machine rates some higher than others and it says "replace" on some brand new tubes.
     
  4. DaveKS

    DaveKS Member

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    Sockets a little wonky, some tubes with bent pins not making good contact or maybe the JJ thin tube pin syndrome?
     
  5. Figaro

    Figaro Supporting Member

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    Checked and all the pins are making good contact.
     
  6. Blue Strat

    Blue Strat Member

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    As long as SOME of the same type test in the ok range, then the others are (wait for it!).....weaker. If they still sound ok then use them. Your tester may not be calibrated correctly or may have never been up to the task in the first place.

    I trash anything that tests weak in my testers...but I'm guessing that my testers are of higher quality. What tester are you using? Which specific tubes are testing higher and lower?

    FWIW, I've never seen ANY tester that gave expected (as per the manual) results for EVERY tube type/number. Sometimes you have to test 30 new examples of a particular type/number to get a feel for what a good reading, actually RANGE of readings, should be.
     
    Last edited: May 21, 2015
  7. swiveltung

    swiveltung Member

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    If they are pre tubes/9 pin. It's often the case. I cant figure it out. I have two testers. Many import 9 pins don't test. Especially Mullard RI. Tubes are fine in the amp. WTF?
     
  8. Blue Strat

    Blue Strat Member

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    Zero readings or low readings? What tester? The only thing that stands out for me is JJ preamp tubes consistently testing lower than ANYTHING else...new or NOS.
     
  9. swiveltung

    swiveltung Member

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    As I remember, readings jump around, or start good and then the needle trickles down fast . Both are BK small format testers.
     
  10. Blue Strat

    Blue Strat Member

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    Almost sounds like a pin connection issue.
     
  11. swiveltung

    swiveltung Member

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    Yeah it does. Problem is, when it occurs, if I stick a OS tube in reads fine. Pin size seems fine. Doesn't change by wiggling the tube either. The jumping around could be the test switch on the BK testers. I've tried cleaning them. But the test level trickling down ...probably not.
    There was a thread a couple years back about this, cant remember if here or Weber forum. Something to do about using higher voltage when testing to burn the tube in or...? Not sure if it was valid or not...
     
  12. DaveKS

    DaveKS Member

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    Are you sure about that. Get you some gold and some little dental proxy brushes to clean and condition sockets. I also use it to coat all pins on the tubes going in tester and in the amps. GX2 safe up to 500°. Just a very light cleaning/coating is all you need unless your sockets/pins are really corroded, then it's time for the D100.

    [​IMG]

    Also what mains voltage are your testers designed to run on? Mine are older too and designed for 115v, I use a little cheap APC voltage regulator set to 117v and make sure I never feed it the 122v+- that comes out of walls here.
     
  13. Figaro

    Figaro Supporting Member

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    Thanks, but all the pins are making good contact in the tester.

    What happens is that some brand new 12AX7 tubes start off in the Good section on the meter and then slowly drop to Bad. They still work in an amp so I guess those are weak? Other 12AX7s stay in the meter's Good section.

    Doesn't anyone else find brand new tubes that test bad, or weak?
     
  14. RussB

    RussB low rent hobbyist Silver Supporting Member

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    What kind of tester is it???


    I have a B&K 667 which is a pretty basic device. I had to get a "feel" for it. For instance, 60 to 70 is average for a new 12AX7. A NOS long plate Sylvania will hit about 80. A new 5751 will be around 60-65.

    It's even less useful for power tubes!



    [​IMG]
     
  15. RussB

    RussB low rent hobbyist Silver Supporting Member

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    The sockets are dirty and/or loose. At least that was the issue with my tester. AES sells socket savers for all the basic tubes
     
  16. swiveltung

    swiveltung Member

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    My testers are both Dyna Jets. Both have socket savers on the 9 pin already. I forget which models but different than the one shown above. One of mine might be a 606...? I replaced the tube inside to no avail (regarding the new import tube testing issue). I don't worry about it much, I find tubes testers of little use anyway, due to different brands testing at diff levels ... and the biggest issue with pre tubes is microphonics which most testers don't do anyway.

    I worked on a friends HRD a couple months back. It would crackle loudly sometimes. tested his tubes and one Fender 12AX7 tube tested bad. I replaced that and played it for about half hour with no issues. First time he used it.... it crackled again. Long story short, the other 12AX7 (which tested fine) was bad. I replaced that and he's been playing it for two months with no issues. Sockets looked tight and clean in the first place.

    IME the hottest testing NOS AX7's are GE. The lowest RCA. And they can be pretty consistent.
     
  17. J M Fahey

    J M Fahey Member

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    Those symptoms point to a bad tester, rather than bad tubes.

    Basic testers are Emission Testers, the logic behind them is that as tubes wear out, cathode covering evaporates, and so less and less useful electrons are available ... similar to choking off a fuel line, the engine will progressively work worse and worse, and eventually stop.

    So cheap testers use the crudest one: they have a relatively low voltage secondary (think 100VAC or so, not actual amp 300/400VDC), connect the tube as a diode (often shorting together grids to plate= "big" anode and cathode used as such) in series with a meter, they read the current and calibrate the "mA" scale in Good/Bad areas.

    Not as bad as it sounds, it's better than nothing (duh!), was enough for TV repairmen and even some Electronics shops had a free use one on the counter (I have seen and used them some 30/40 years ago) because regular people would bring bags of tubes, test them, and buy replacements on the spot.

    But consider that the Good/Bad scale does not have any precision, and even if it were calibrated, doubt it would fit *all* tubes.

    That said, tube emission does not vary by the minute, it's a long process, so if a tube starts good and gets bad in a minute or two, I'd MUCH suspect the tester itself.

    Maybe filament voltage isn't stable, or applied "high" voltage drops, or some connection is poor/corroded/dirty , even the sockets as suggested or one of the complex multi switches may have worn/weak contacts, who knows?

    If anything, tubes should start "bad" and end "good" as they warm up, not the contrary.
     
  18. Figaro

    Figaro Supporting Member

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    The tester I used was an old Mercury Model 202 with a large Good-Weak-Replace meter on it. It's just a basic emission tester. When I tested a bunch of brand new 12AX7s at the same time, some registered 70 to 80 Good on the meter and held steadily there. Others registered around 60 and then slowly dropped to the Replace section of the meter. So how could it be that the tester is bad?
     
  19. RussB

    RussB low rent hobbyist Silver Supporting Member

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    because you said the tubes sound fine in your amps
     
  20. Figaro

    Figaro Supporting Member

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    Then why do some test good and strong?
     

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