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Re: Stupid question about tube testers

Posted by Mechans (A) on March 15, 2007 at 16:25:52

In Reply to: Stupid question about tube testers posted by izquierdaste@hotmail.com on March 15, 2007 at 15:23:37:

When you mean set you are referring to the "english" good/bad delineation on a TV 7. The meter is pretty much self explanatory despite the fact that numerical values are provided. I don't think there is any microhmos reading available to give you a better idea of how well the tube is functioning. The scale I recall is 65 to hit the green zone anything less is supposedly marginal. When tubes were plentiful I am sure the intent was to get you to replace it.
I have used tubes that measure low. They sound good in some cases which throws the whole meaning of testing to decide on sonics into doubt. Ask Jeff Behr we have both had similar experiences using completely different testers. (they must match if using 2 channel dual mono signal pathways)
That said, many that test bad are truly bad- really dead or fried. The 100 on the TV DU 7 is not the new tube value that should be in the setting book. I have watched a dealer use his carefully maintained and frequently expert calibrated DU 7 to test batches of new tubes of all types. They are either duds or measure Green/Good from 70-90. Its really a yes /no deal.
If you want precision testing you need to climb into the stratospherically priced computer tracer devices.
I use a run of the mill 1961 Hickock 800 which needs to be calibrated at the moment but prefer the MTC microhmos values it reads. With those testers the nominal new or 100% value is given on the roll chart. Your setting booklet should give you the same type information but I have to see the next time I visit.

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