Mpfffff.... Tube Testers. Mpffffff.........
OK - this is from an old post in another venue, and mostly focused on vintage radios, but applicable here:
Basic stuff with a lot of generalizations and special-nature stuff
Tube testers overall come in two groups: Emissions Testers and GM/MC
(Mutual Conductance) testers.
Emissions Testers: The much-simpler of the two types, these measure the
"Edison Effect", whether there is any electron flow between cathode and
anode. As this is the least any tube must do in order to work at all,
the accuracy of this single measurement is limited as to the actual
performance-in-place of the tube. IN 99-44/100ths% OF ALL APPLICATIONS,
AN EMISSIONS TESTER CAPABLE OF "SHORTS" AND "GAS" TESTS will be more
than adequate for all vintage radio work. See below on Shorts and Gas.
GM/MC testers: These tester types measure 'gain' on a tube against a
scale centered on the 'average' gain required for such tubes, and under
specific parameters including bias((usually) negative voltage applied
to the grid). Emissions is assumed or there would be no gain, so these
testers give a far more meaningful picture of tube performance under
actual operating conditions. IF YOU WILL BE DOING EXTENSIVE AUDIO WORK
OR FEEL THE IRRATIONAL NEED TO MATCH TUBES, then a GM-type tester is a
necessity. See "Other measurements" below.
Shorts: No tube tester should be considered under any conditions that
does not have specific and panel-marked settings to test for Shorts.
Some shorts will not show up with a cold tube, so a simple VOM will not
show all of them. Repeat: If a tester does not have clear, specific
"SHORTS" testing procedures, reject it.
Gas: Some tubes become gassy over time or are gassy... either from
leakage through the pins, poor manufacturing, a bad 'getter' or
similar. gassy tubes can wreak havoc due to high-voltage 'leaks' and
other problems. Testers should have a way to detect gassy tubes, also
clear and specific. Reject any that do not. Note that these tests may
be complex, but they must be there.
Life: Smoke and mirrors for the most part. Drop the filament voltage by
one setting or reduce the line-in voltage by 25% or so, you will get
the same results on the meter. But a nice addition if everything else
is there first.
Other Measurements: Some testers will measure or allow to be measured
Plate and/or Filament currents. Some will allow the addition of an
external bias resistor. These are necessary if "matching" is to be
done, but not relevant much to vintage radios.
Limitations: Not all testers do a great job of measuring high-demand
tubes such as a 6550 amplifier tube or an 83 mercury rectifier tube.
The typical vintage radio person will seldom see either.
So why have a tube tester in the first place?
Mpffffff..... well..... they can be nifty things to show off, all those
sockets, settings, knobs and other mad-scientist aparatus. But the
brute fact of the matter is that in most cases the best test of any
tube is the gear it is in. All that aside:
- they are useful for go/no go decisions, based on intact filaments,
shorts and gas.
- they will allow you to screen tubes before installation or detect bad
tubes prior to troubleshooting.
- under some conditions, they will indicate potentially bad tubes or
point towards potential failures due to bad tubes.
- if one does extensive audio work, or works with expensive or rare
tubes or chooses to match tubes or has any of several other unusual
requirements, then an MC tester will be required. This is the
So, to sum up (and a lot of my *opinion* sneaks into this):
Tube testers are largely luxuries as instruments, to be purchased
_AFTER_ a good isolation transformer, a properly metered Variac, a very
good VOM, a good signal generator, even after a good signal tracer.
Equal to a full-voltage cap tester, but before an Oscilloscope, just.
A tube tester *MUST* have clear, specific tests for shorts and gas.
Harp, harp, harp. Without them, it is useless for any practical
Sencore, Heath and Simpson make some very nice emissions-type testers
with all the required tests as noted above. Others do as well, but
sometimes the brand-names are just better, easier to use and better
supported. The three named above are extremely well-supported,
up-to-date charts are readily available and they are fairly robust.
Hickok, Stark, Eico, Heath, Supreme, Simpson, AVO and others make MC
testers. Hickok is considered to be the TOL, with specific reference to
the 539C. In point of fact, the good 'names' all make good testers, but
Hickok has the best support-in-detail and reputation. AVO if you are in
Thing to keep in mind: There was a point when every back-street
instrument maker was making tube testers for home use. And even some of
the better 'names' chose to cash in on the post-war consumer
electronics craze. A great deal of crap got out into the market and
resurfaces every day. Unless you know what you are doing, DO NOT
purchase a tester sight-unseen, especially from an unknown or untrusted
I keep a properly calibrated Hickok 539B and a very nice Simpson emissions tester. The former has become increasingly useful as I shift from 95% vintage radio stuff to about 50:50 radio/audio as of late. With additional instrumentation (two VOMs) I can now match tubes very closely, and, yes, it will drive a 6550. The Simpson handles the vast bulk of my radio needs as - and I repeat - the best test of any tube (other than shorts and gas) is the radio needing it.
Were I looking for a tube tester today, would I drop the probably necessary $1,200 - $1,500 for a properly calibrated and reliable Hickok 539-series? Not likely.
Of course, now that I have these beasts, and it has gotten out into the 'community', I average about a visit per month from those needing tubes to be tested. And there is usually a line at Kutztown.http://tone-lizard.com/tube-testers/