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!

©1995-2017 Philip I. Nelson, all rights reserved