On Hickok Mutual Conductance tube testers, the test data books (or rolls) always show the mutual conductance value expected for each tube. However, I noticed that many times these values are not the same as the values I see in various tube specification books and sometimes they are way off.
For example, my 533a tester lists a 7189 beam power amp tube as expecting a mutual conductance of 7500 but several spec sources says it should have a mutual conductance of 11,300.
Does anyone know the way to use the hickok expected mutual cond. numbers? Are they average expected, used expected, new expected, best case or minimum pass expected?

Thanks for any help at all you can give me.

The short answer is that Gm depends on plate current. The tube-manual figures are at normal operating conditions, but a tube tester may not happen to bias a tube at that level.

The long answer is to look at the "transfer" or "mutual" characteristic: plate current on the vertical axis, plotted against grid voltage on the horizontal. There will be one of these curves for every chosen value of plate voltage, similar in shape but displaced sideways on the chart. The slope of the curve at any point is the Gm at that point: the slope gets steeper as the plate current increases. Not many tube manuals show transfer curves: the GE industrial manual and the WE manual both do, or they could be created by re-plotting the information on normal plate-family curves.

George,

"For example, my 533a tester lists a 7189 beam power amp tube as expecting a mutual conductance of 7500 but several spec sources says it should have a mutual conductance of 11,300."

My Hickok 6000A roll shows the 7189 as having a Gm of 6000. I assume it uses slightly different test conditions then your 553a or the tube manual, (as suggested by Alan).

Greg

Ok, I can understand that the Hickok is testing under different conditions/voltages than the setups outlined in the tube characteristic/specifications books. In fact I'm pretty sure even the filament voltages are somewhat lower in the Hickoks because generally the tube filaments glow much brighter on my emission-type Heathkit tester than they ever do on my Hickok.

So, I just have one question then: are the mutual conductance numbers given in the Hickok manuals/rolls the optimum expected GM for a "new" perfect tube and than any used tube would have to be decided by the user (person testing)how much below that number would be ok?

Thanks for the help everyone. If nothing else, this certainly is an ongoing learning opportunity.

-George

Hi George

Tubes should test to the number specified or higher. New tubes may test twice the number.

Norm

: Ok, I can understand that the Hickok is testing under different conditions/voltages than the setups outlined in the tube characteristic/specifications books. In fact I'm pretty sure even the filament voltages are somewhat lower in the Hickoks because generally the tube filaments glow much brighter on my emission-type Heathkit tester than they ever do on my Hickok.

: So, I just have one question then: are the mutual conductance numbers given in the Hickok manuals/rolls the optimum expected GM for a "new" perfect tube and than any used tube would have to be decided by the user (person testing)how much below that number would be ok?

: Thanks for the help everyone. If nothing else, this certainly is an ongoing learning opportunity.

: -George

Heater voltage should be +/- 5% for any tester, but some makers weren't as fussy as others. If you're looking for tubes nearing the end of their life, you want to keep heater voltage on the low side.

: Heater voltage should be +/- 5% for any tester, but some makers weren't as fussy as others. If you're looking for tubes nearing the end of their life, you want to keep heater voltage on the low side.

: On Hickok Mutual Conductance tube testers, the test data books (or rolls) always show the mutual conductance value expected for each tube. However, I noticed that many times these values are not the same as the values I see in various tube specification books and sometimes they are way off.
: For example, my 533a tester lists a 7189 beam power amp tube as expecting a mutual conductance of 7500 but several spec sources says it should have a mutual conductance of 11,300.
: Does anyone know the way to use the hickok expected mutual cond. numbers? Are they average expected, used expected, new expected, best case or minimum pass expected?

: Thanks for any help at all you can give me.

I have spend the last 30 plus years trying to find the best way to test electronic parts, it magical.
The first five years were spend on vacuum tubes at a
TV/ tube manufacture, and last the 25 designing test equipment to test solid-state devices.
A book that cover the variability in tube properties is MIL-HDBK-211 Military Handbook Electron tubes, Techniques for application of in Military Equipment a must read for someone testing and building tube
equipment.

The tube in data book curves come from a product distribution curve and /or lot distribution curve sampling, that why most date sheets have words like TYPICAL or AVERAGE on them.
Even the best of the tube tester manufactures never tested every tube type
From every tube manufacturer in their tester.
A book could be wrote on this, but it all comes down to trade off's in the Testers because of cost. The bigger ??? to ask today is what happen to all
Tube that were just outside of past curve , that were sold as SECONDS. At some time this could be has high as 50% of a production lot.
A data book is just a starting point.

Jimmie