[95bcwh]

All,
 As I'm shopping for tubes, I saw thousands different kind of measurements being reported.
Examples:
(1) a so-called 'matched pair' measured at 2000/1750 and 1800/1550 on Hickok 6000

(2) another 'matched pair' measured at 83/85 and 85/83 on B&K Model 606

(3) another 'matched pair' measured at 95/97 and 96/97

Is there any general rule of thumb on how to interpret them?

Thanks for helping out.
barry


 

[tonyptony]

Barry, short answer:no, long answer:yes.

First things first. Go here

http://www.tone-lizard.com/Tube_Testers.html

and read all about tube testers. Once you do that you will see that, for true mutual conductance type testers, the reading will be either against a gm scale or will be some type of linear scale for that manufacturer. B&K testers, for example, often use a linear scale that goes to 120. There is no real way to correlate the numbers on a B&K tester to the gm number on many of the Hickok testers. Most of the Hickok mutual conductance testers read out on a gm scale (mmhos). Bottom line is you have to know what "good" is for a particular tester. My B&K 707 uses a linear scale, and for most tubes a reading of 65 is considered minimum good. So if someone is selling tubes that test 100/100 on a B&K 707 I would have a good sense that they test pretty darn well.

BTW, when you see two numbers, x/y, that is typical for dual triode tubes. Each number is for a given triode section in that tube. You'd like those two numbers to be usually within 5% of each other for a real nice tube.