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Tube testsets
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Author:  Gimp [ 03 Aug 2009, 18:09 ]
Post subject:  Tube testsets

Can anyone explain to me why a test set that displayed Conductance in micro-Mhos (eg Hickok) would be more desirable than one that displayed it as a percentage of ideal value (eg Simpson) for the tube being tested, given that both test sets were of the comperable quality? (Don't compare Heathkit to Simpson and expect the same quality.)

It would seem to me that both are displaying the same information, but in different formats. For the Hickok one would have to know the tube specifications to know if conductance was within speck.

Matching of tubes should be the same on both with the possible better resolution on the u-Mho scale vs percentage. If the scale resolutions were the same even that would be moot.

Or am I missing something?

Thanks.
Steven

Author:  Gio [ 03 Aug 2009, 20:53 ]
Post subject:  Re: Tube testsets

Hi Steven,
An emission tester will only give you a basic idea of what condition the tube is in. With a tester that will measure transconductance you will be able to "match" tubes.
Cheers

Author:  Gimp [ 03 Aug 2009, 21:10 ]
Post subject:  Re: Tube testsets

I invoked my Google skills and found radiolaGuy.com had a good explanation along with some instructions:

http://www.radiolaguy.com/Mutual-Emission.htm

Looks like I'm better off saving up for a Hickok.

If you can suggest any other manufacturers or sites, I'd appreciate the links.

Thanks.

Steven

Author:  Gio [ 04 Aug 2009, 12:14 ]
Post subject:  Re: Tube testsets

Hi Steven, here is another good page: http://www.tone-lizard.com/Tube_Testers.html
and it lists a few makes of the popular mutual conductance testers

Author:  Gimp [ 02 Sep 2009, 11:40 ]
Post subject:  Re: Tube testsets

I settled for a Mercury 1000 test set.

Overall it is in very good condition. I had a problem with it giving erratic results that continued to get worse till it quit completely. I finally found a bad 270 ohm resistor (open). I replaced it and used the Mercury 2000 cal procedure as the 2000 has basically the same schematic as the 1000, with a transistor checker added (Step 3.B calls out partial incorrect info, diode neg is to pin 8 not pin 5) It looks like it is working properly now.

I tested my 6146(B)s and found they are all below spec for Gm, so I'll shelve that project before starting.

I just got a batch of Svetlana 6P1P-EV beam power Tetrodes that all test fine (lowest Gm 3900, most between 4200 and 4400). I'll use them to make a stereo PP amp as a first design project.

Author:  Bluesman [ 02 Sep 2009, 15:30 ]
Post subject:  Re: Tube testsets

Is it possible the tester needs to be calibrated? If you bought it used and it hasn't been checked out, I wouldn't put too much faith in the accuracy of the results.

Cheers, Greg

Author:  Gimp [ 02 Sep 2009, 16:37 ]
Post subject:  Re: Tube testsets

I performed calibration per the Mercury 2000 manual, and verified it a commercial 6L6 cal tube.

All adjustments still had the original paint on them to prevent movement, so it had never been adjusted since it left the factory. I have three NOS 6BA6s which all measure within 10% of each other that I used to confirm the adjustments.

The only other thing I can do is to take the 6BA6s and build a test circuit based on Class A design specs for the tube, and measure the Gm in actual operation. Then compare the results to the indicated Gm from the test set.

I'm open to suggestions.

Author:  Bluesman [ 02 Sep 2009, 17:50 ]
Post subject:  Re: Tube testsets

Sounds like you covered all the bases. The 6146Bs are probably just as tested.

Good luck with whatever project you settle on.

Cheers, Greg

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