[Andrew Pielet]

So, why do all tubes have different testing numbers? I understand that all tubes are not the same (but some are matching), But why do the same exact tubes have completely different #'s? Example: 44/47 47/44. Then why would a different tube (same brand, etc.) be 2150/2050? I know they are close enough to be matching, but why such a huge difference in #'s? Is it the testers themselves that have completely different scales? Are there 2 measurements?
Thanks

 

[vwap]

Quote:

Originally posted by Andrew Pielet So, why do all tubes have different testing numbers? I understand that all tubes are not the same (but some are matching), But why do the same exact tubes have completely different #'s? Example: 44/47 47/44. Then why would a different tube (same brand, etc.) be 2150/2050? I know they are close enough to be matching, but why such a huge difference in #'s? Is it the testers themselves that have completely different scales? Are there 2 measurements? Thanks

From what I understand, the two measurements are measures of the two sections of the tube. The large difference in numbers is attributed to the tube testers themselves, which vary in scale, and what it's actually measuring...

 

[Andrew Pielet]

My question for the most part is "I know they are close enough to be matching, but why such a huge difference in #'s? Is it the testers themselves that have completely different scales?"
Do I need to know the scale of every tester to know what life is in a tube?

 

[SumB]

Quote:

Originally posted by Andrew Pielet I need to know the scale of every tester to know what life is in a tube?

Yes and no. You need to know what the reading means, but most sellers will lay it out in the listing.

As to why they differ so drastically, regular testers can have varying scales indicating the percentige of useable life left in each section of the tube - this can range from 0-50, 0-100, 0-120, ect. For instance a 44/47 tube would test at 44 for section one, and 47 for section two. These are your most basic tube testers.

Mutual Conductance, or transconductance testers, display in micromhos, and some can even report the mA. These are your most advanced form of tester, with the most exacting readings (assuming proper calibration). So a "2150/2050" figure would be the micromhos of each section as reported on a transconductance tester.

 

[Andrew Pielet]

Thank you, BIG help.

 

[Hirsch]

Quote:

Originally posted by SumB Mutual Conductance, or transconductance testers, display in micromhos, and some can even report the mA. These are your most advanced form of tester, with the most exacting readings (assuming proper calibration). So a "2150/2050" figure would be the micromhos of each section as reported on a transconductance tester.

Yes and no. Some mutual conductance testers will report micromhos (Hickok's come to mind). However, not all mutual conductance testers will measure tubes the same way, or arrive at the same result. For example, the B&K 747 simply reports mutual conductance as a percentage of an ideal tube, in theory. In practice you need to test a bunch of tubes just to figure out what new tubes actually measure in order to be sure exactly what you're seeing. That assumes that you've kept the tester in perfect calibration (I do). Many testers can fall out of calibration easily, and results become meaningless.

An emission tester sends a signal to the tube and measures the output. This can be measured as a percentage of ideal, or in mA, or some other scale. The problem with this is that it's not what tubes do in real life. A mutual conductance tester measures the change in output of a tube relative to a change in input voltage: it's ability to amplify. This is closer to what most tubes are actually doing and is a better measure of how a tube is likely to perform in an audio application.

In practice, you need to get the operating characteristics of the tube, but this is more information than a buyer really needs.