help with calibrating a Tv7d/U military tube tester

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Hello,
I received a Tv7d/U military tube tester from a friend's estate (husband passed, wife thought I might like to have it). I have read the manual through and though and have learned how to test tubes with it. I think it is not calibrated well though. I am finding tubes that are new and/or recently tested at over 100% by other testers only test at sometimes 30 to 60% of expected. In fact off all the tubes I have tried to test with it I have found they all test well below where I would expect them to test.

I have searched around a little on the web about calibrating these but have come up empty handed. Can anybody give me some advice about this or tell me how to do it? I would even consider paying someone to calibrate it for me.
Thanks for your help,
Jeff
 
Do you have any of the service manuals (T.M.s in military speak)? The alignments are not hard at all provided you have some basic test equipment (DMM, an isolated 50VAC source, and some resistors). The only snag in following the manuals is that are based on OLD analog meters that draw more current than a modern DMM and the measurements and adjustments take this into account. The first step is to find the manual, "TM 11-6625-274-35" is the one you need. Is this the one you have?

Craig
 
Hello,
I received a Tv7d/U military tube tester from a friend's estate (husband passed, wife thought I might like to have it). I have read the manual through and though and have learned how to test tubes with it. I think it is not calibrated well though. I am finding tubes that are new and/or recently tested at over 100% by other testers only test at sometimes 30 to 60% of expected. In fact off all the tubes I have tried to test with it I have found they all test well below where I would expect them to test.

I have searched around a little on the web about calibrating these but have come up empty handed. Can anybody give me some advice about this or tell me how to do it? I would even consider paying someone to calibrate it for me.
Thanks for your help,
Jeff

If the readings differ that much then it's likely more than calibration that's at fault. A couple thoughts:

Have you checked the 83 and the 5Y3?

Also - keep in mind the reading from one tester cannot necessarily be compared to the reading in a second tester. Are the other testers mutual conductance types or just emission testers? The TV-7 is a mutual conductance tester, so comparing it to emission testers isn't valid.

Be sure you have the TV-7 set up properly, and the AC line voltage rheostat properly adjusted.

If you can give a couple examples of the "new" tubes you tested and what they read on the TV-7 it would help. Also the brands and models of the other testers may be of help.

If I may - if it does need calibration do two things:

1. Be sure it's properly repaired (if repairs are needed) before calibration.

2. You can also substitute a solid state rectifier for the 83 (leave the 5Y3 in place). The SS replacement means a much cooler running tester and it'll never need replacing. If you don't have a source for them drop me a note.
They rarely affect calibration of TV-7s, but it's best to calibrate it with the sub in place.

That's a very good tester - it's worth making it right.
 
Like the TV2, the TV7 series is slightly more strenuous in it's "what's ok" for Government work. Because of it's small size and military clothes, it has obtained cult status with many people. But IMO it is less of a tester then many others. And I have owned most all of them at one time or another. One drawback to the TV-7 is the fact that readout is in percent quality (0-120 scale) rather than Gm (µmhos). so translation is necessary to compare to manufacturer's Gm values.


Not withstanding, there is one area of calibration that is virtually never mentioned in any manual procedures, for any makes. And this is calibration of the line test, or line set position on the meter. Rather then type it all here, I'll refer you to the link below.

Overlooked calibration:
http://www.radiolaguy.com/PDF_Files/Overlooked_tube_tester_calibration.pdf

A good general overview of tester calibration:
http://www.radiolaguy.com/PDF_Files/Hickok800-800Acalibration.pdf

Edit, forgot this for the TV-7
http://www.radiolaguy.com/PDF_Files/TV-7 Calibration.pdf
 
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Hey thank everyone...
Just for starters the tubes I have tested with mine were tested on various different testers, most using gm rather than emission. I couldn't possibly recall or figure out which tubes were tested by what now. I can say that tubes I have purchased recently from very reputable sources and had tested 100% or better in every respect by the sellers......these also tested well below what I would expect, even though I realize a direct comparison cannot be made (i.e. we are talking about an order of magnitude in some cases where a perfectly new tube will test at 30% of expected).

I didn't even realize these had tube rectifiers in them! I haven't yet opened the device up.

So, if I replace the 83 with a SS rectifier will I need to add a dropping resistor to account for the higher efficiency of the SS rectification?

I will read al the sources provided above....as to which TM I need, I would have to take your word that the one mentioned above is the one I need. All I can say is what model I have. The little book that came inside the tester only has information pertaining to tube testing instructions and parameter settings. I have followed the instructions on the line test as stated in the book....they are straightforward but I will review the link above to see if there is anything additional I need to be doing.

Bottom line is if I replace the rectifiers (if bad) and I still can't figure out how to get it working correctly I will pay somebody to do it for me (hint, hint).
Thanks again,
Jeff
 
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Where can I find a decade resistor? Also, what is it? It appears to calibrate m tester I need one of these. I seems to be some sort of variable resistors with extremely high resistance values (up to 15 meg). Either way, I guess I will be needing one of these so any help in acquiring one would be greatly appreciated. BTW, thanks for the link HollowState, this appears to be exactly what I need (testing/calibration manual), I just hope it is all I need in terms of know how.
Jeff
 
Where can I find a decade resistor? Also, what is it? It appears to calibrate m tester I need one of these. I seems to be some sort of variable resistors with extremely high resistance values (up to 15 meg).

A decade resistor is a box with one or more rotory switches that contain resistors in incremental steps. They are usually close tolerance wire wound resistors and quite expensive unless you get a low quality one like a Heathkit. But a decade box is not totally necessary, it just makes things easier. If you have a pair of clip leads and a supply of loose resistors, you can get by with them. It just takes a little longer and it's more tedious because you have to clip and unclip the resistors. You'll also need to be very carefull if you work hot. Look to eBay for one or perhaps borrow one from an electronic friend.

A search of the web will yield repair services like "alltubetesters" dot com. (I know nothing about them and not affiliated)
 
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