Supreme Model 589-A Tube Tester
I bought this funky old tube tester for $10 at a radio swap meet.
A couple of weeks earlier, I had made a deal at a garage
sale to buy
several boxes containing over 400 old radio tubes for $10. So
I needed something that would help me cull out the dead tubes.
This is an inexpensive "emission" type tester. That
is, it tests whether a tube is emitting enough electrons
to qualify as "OK." This is not a very sophisticated
test. Tubes do various other things, such as oscillate, which
aren't well represented in an emission test. More elaborate
conductance-type testers can tell you more about a tube's condition, but they cost quite a bit more than this type.
When I bought this item, its linen
case was pretty moldy. I gave it a vigorous scrub inside and out
with warm soapy water. Even the cloth-covered internal wiring was furred
with mold, so the innards got a careful but thorough cleanup
with a toothbrush, as well. Then I left it out in the hot sun for an
entire day to dry things out. The linen case still smelled mildewy after that, so I wiped on a thin coat of fine oil finish to seal
it up and keep things fresh for a while.
The little window at bottom center contains a
roll chart giving test information for common tubes of the time.
You select the tube by rolling a thumbwheel to the right of the window
until the tube appears. Then you follow the red arrowed lines up
to the four rotary switches and set them to the values shown in
each column of the roll chart. The dial at top center shows the
test results.
A tube tester is not really essential for a beginning collector.
Contrary to popular belief, tubes are pretty durable items. Sealed in a vacuum, a tube won't go bad just from sitting around.
In my experience, when you buy an old tube radio, most if not all of its tubes will be good. So you shouldn't automatically replace them all just for the heck of it. I never replace a tube unless
I have clear evidence that it's bad.
Testing Tubes Without a Tester
If you don't have a tube tester, there are other simple
ways to check a tube's condition. In a radio with a transformer type power supply, look at the tubes. The good ones will be glowing. If one of them doesn't glow, it's bad.
In a radio with an AC/DC type power supply, if all the tubes light up, then none of them is a dud. If all of them are dark, then one or more is likely a dud, since in this type of radio
all of the filaments (heaters) are connected in series.
(This condition could also be caused by other problems in the
power supply, such as a broken power cord or blown fuse, so
"all dark" doesn't always signify a bad tube. Also note
that the 1-volt tubes used in battery portables such as the
Zenith TransOceanic don't glow visibly; their normal operating voltage
is too low.)
Some tubes have metal cases, preventing you from making
a "glow" test. These tubes, or any tubes for
that matter, can be dud-tested with an ohmmeter. First, look up the
tube by its type number to find out which pins are the
filaments. If you don't have tube reference book, you can
look it up online at Nostalgia Air and
various other websites.
If you measure infinite resistance between the two filament
pins, then the filament has burned out and the tube is dead.
If you measure a low resistance, then the filament is good.
A tube with a good filament should light up, in short. However,
if it has been used a lot, it still might be so weak that it
doesn't function well.
The best test of all is to put a tube in a working radio (or
other tube device) and see whether it works as well as a known-good tube in that position. If it does, then the tube is usable
in that application,
regardless what the fanciest tester might say about it.
For example, say that I have a working radio that uses a type
6SH7 tube, and I have just brought home another radio that uses the same tube. If I take the suspect 6SH7 from the new radio and plug it into the
working radio, then the tube is good if the radio plays normally.
You can also do the opposite kind of substitution. In the
previous example, say that the new radio doesn't work correctly
and you suspect that it has a bad 6SH7 tube. You can substitute
the known-good 6SH7 from your working radio to quickly test
this hypothesis.
To avoid confusion, check only one tube at a time. If you pull them all out at once and mistakenly plug them back into the wrong sockets, your radio probably won't work at all!
There are hundreds of different tube types, so there's no guarantee that you can test every one this way, unless you have
a huge assortment of working radios in your house. Radio designs
became quite standardized over the years, however, so you will
find that many radios use the same tube "lineups."
After owning this tester for a couple of years, I acquired
a couple of better ones and disposed of this at a local swap meet.
I sold it for $10, exactly what I had paid a few years before.
Simple old testers like this are very common, so if you can't
pick one up for $20 or thereabouts at a radio swap meet,
you're just not trying!
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