*Tube Testers*
By: Ziggy
26 October 2006

Many people are discovering the joys of collecting and using the fine old "Boatanchor" shortwave and Ham radio equipment made with tubes. I get asked fairly often for advice on which tube tester to buy. The old time radio repairmen always said that the best way to test a tube is in the device that uses it. But you sure don't want to put a shorted tube in your nice old receiver, so you really need a tester. And a tester allows you to sort out a bunch of tubes that you may not have a radio for.

First, there are two types: Emission testers and Mutual Conductance testers. The Emission testers test the ability of the cathode in the tube to produce electrons. As a tube ages, this ability decreases so this test is a kind of remaining life test. This is the only kind of test for rectifier tubes, and is very worthwhile for transmitting tubes. The Mutual Conductance testers were mainly produced by Hickok. They test the ability of a tube to amplify signals, and often use a reduced heater voltage as a remaining-life test. I have both types of testers, but if I could only keep one it would be Mutual Conductance.

So which one to buy? IMHO, the main consideration is the amount of testing data available. Hickok did the best job of keeping up with the new tubes as they were released, and maintained a regular update service for their roll charts and data books. The models 533A, 600A and 605A use the same test data. I have been able to collect the most coverage for these three models. The 800 and 800A use the same data. I have found almost as much data for them. The 539B and 539C also have a lot of test data available, but these testers are the favorites of the stereo nuts, and bring sky-high prices. I would also pass on the 6000 series because there is not quite as much test data available as for the previously listed models.

Heathkit made one really nice Mutual Conductance tester, the TT-1. I had one for a while, but I sold it because the available test data books didn't cover enough tubes and there was a problem with oscillation of some of the common stereo tubes like the 6BQ5 when trying to test them. Hickok has some pretty strong patents on their test circuits, and I suspect Heathkit may have had some trouble designing around them.

Hickok also designed several ultra-high quality testers for the military. They were basically standard Hickok circuits but had the very best build quality. No expense was spared in selection of parts. The transformers were much bigger & better, they used mainly ceramic sockets, and the potentiometers were top-quality Allen-Bradley units that costed five bucks when the Clarostat units used in Hickok's regular models costed fifty cents. They all came in heavy metal cases with rubber gaskets. Again, test data is the main factor for me. The winner is the TV-7 series. Nolan Lee has made a big project of collecting all available data for the TV-7, and he gives the file away on his web site. There were four models: A, B, C, and D. The differences were slight improvements. I would skip the A model because it is the oldest. The B & C models are the best buys. The D model commands a substantial price premium because the range switch has an extra position, but it only allows testing of a few oddball tubes used in military equipment. The best thing about the TV-7 is that you can get the Army Depot Repair Manual for it. This is a very comprehensive manual that will enable any decent technician to troubleshoot the TV-7. The I-177 was designed before WW2, and is only good for testing antique tubes. Hickok made the MX-949 breakout box for the I-177 after WW2 which allowed for testing newer tubes, but this was a stopgap measure and there is a lack of testing data for postwar tubes. There were several other military models such as TV-2, 3, and 10 but it is best to stick with the TV-7.

It is very easy to find tube testers on Ebay, but you are likely to pay top dollar and could end up with a tester with problems. It is much better to go to a Hamfest . You can see (and maybe even test) what you are getting and you will almost certainly get a better deal. You can find a Hamfrst calendar at www.arrl.org.
Ziggy



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