The difference between a simple
emission checker (like a Heath TC-1, 2 & others) and a mutual
conductance* checker is very important. An emission checker tests for
shorts & cathode (or filament) emission only. The meter reading gives a good-bad
reading by virtually tying all the elements of a vacuum tube
together (except the cathode & heater) and testing the tube for
cathode emission by subjecting it to test as a diode (or
emission checker will basically tell you whether a tube is
usable or not and give you an indication how strong is the
cathode emission. Both types will do a good job testing for
shorts and leakage.
A mutual conductance checker will apply voltage to each element
of the tube, supply bias and a signal to the control grid and subject
the tube to a test much like it may be used in an actual circuit,
measuring plate current and indicating such in micromhos. If you
want to pair up tubes in "matched pairs", this is done
by comparing the "Gm"** reading and finding a pair with equal (or
within 10%) reading. You cannot do this with an emission checker.
This is not to say that an emission tester is of
no value, even the best tube testers can mislead and test a
tube good even though it may not function well in soem circuits.
* Gm.....the symbol for mutual
** mutual conductance....the measure of
alternating plate current (measured in micromhos) in relation to
the control grid signal voltage (simple explanation, it's really
Summing up, if you want a tester
for occasional use for testing the tubes in your own equipment,
you may no want to invest in the more expensive mutual
conductance testers. On the other hand, if you have lots of
tubes and want to sell them on eBay, the mutual conductance
value (as read on a properly calibrated mutual conductance
tester) supplied along with the tubes you are offering is
Basic info on tube testing, click here.
> Calibration tube for Mutual or Transconductance tube checkers-
> Tube tester restoration info- click
Hickok instruction & tube data manuals-
replace Hickok tube tester
tubes with solid state devices?
> Fuse lamps
for Hickok tube testers > click here
testers for sale >
Need a #83 tube >
For free downloads
concerning tube tester calibration, click
Calibration verification test tube
click on for price and ordering details
What is a calibration tube?
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