Bob - That's a very good site reference. Lots of good information there.
The "Life Test" typically just reduces the filament voltage on the tube. This indicates whether the cathode is straining to deliver enough electrons, (wearing out,) or has "life" left! If the meter indications stays steady or only drops slightly, then the tube has considerable life left, at least from an emission standpoint. If the meter drops a lot, not good.
You can perform a similar test on any tube tester, merely switch the filament voltage DOWN one step, i.e., from 6.3 to 5 volts. A "good" tube will drop only a few divisions, while a "weak" one will drop 5 to 10 or more divisions.
73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs <www.k4oah.com> Robert Ladden wrote:
I have had good luck with a Jackson 648A tester. It is not an expensive Hickok mutual conductance tester. It uses a "Dynamic" testing circuit and there is much debate if that is really better than simple emission testing. But it does have a test I have found useful. It has a “Life Line Indicator” test which reduces the filament voltage. It sounds like a gimmick but it seems to work for me. Just last month I had a weak 12AX7 in my T-4XC. It tested good in the regular test, but it was bad in the life test. I replaced the tube and now I don’t have to turn the gain so high to tune up. That test has also worked for me with other tubes. That life test has also been useful for 6JB6’s. It has found soft tubes with the life test that otherwise have tested good. Whether it finds all soft tubes is a question, but it has proven to be a good screener by finding tubes for me that have tested to be soft in my T-4XC (I had a box of unknown tubes). But swapping tubes is by far the best test but at least I can eliminate the "no chance" ones. My Jackson 648A did not come with the 9-pin NOVAR socket needed for 6JB6’s. I added it myself and it was not hard to do using the schematic. One advantage for the Jackson 648 is that Vacuum Tubes Inc. publishes their own manual for it (I have no connection to this company except as a customer). There is an excellent discussion of tube testers at http://www.tone-lizard.com/Tube_Testers.html It is written from an audiophile’s point of view, the only other group still using tubes. 73, Bob WW3QB
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