RANT WARNING!

On tube testers - with the exception of very modern testers that will plot curves on a PC, effectively there are two types of testers and within each type, two tiers.

A top-tier emissions-tester is good for 99-44/100ths of most hobby uses. It is, for the record, very nearly as good as a second-tier GM tester. Better in some few cases.

A top-tier emissions tester will also test (reasonably accurately) for "SHORTS" and "GAS" - which functions are what separate a tester from the device itself. Reject any tester out of hand if it does not do shorts and gas. It is useless in actual practice. A Heath TC-2/3 and many others will meet the most basic needs of the hobbyist. Prices for Emissions-Only testers are, perhaps, 20% of the price of a GM tester, all other things being equal.

A standard GM tester will also test for shorts and gas - some better than others. By virtue of being a GM tester, such a unit will give a RELATIVE indication of actual tube quality against a narrow set of fixed parameters. That information is very nearly useless *unless* one has known-good tubes with which to compare readings.

Now, a top-tier GM tester (and there are very, very few) will allow one to set bias, read filament current, plate current, and - thereby - allow one to actually match tubes accurately. An example of such would be the Hickok 539 series. But NOT (emphatically) a TV7, however popular and expensive it might be.

Unless one is seriously into audio and has an actual need to match tubes and/or do qualitative testing, don't waste your money on such a tester. And, if one is as deeply in as all that, look into the modern testers with curve-tracers and so forth. Big bucks. Or, if, as I did, you should trip over a fully calibrated 539B, grab it. But, at the going rate of $1,000 and up, not so much.

Now, on WHY:

A tube with a short - especially a thermally dependent short can do great harm if it fails in-situ and without the operator right there with the instant shut-down device. A slagged rectifier tube, for instance, can take out a power-transformer in seconds. And why it is that a certain tubes should be tested for some time on a tester to look for thermal faults. Open filaments are seldom a threat, but shorts really, really are. And, a thermal short will NOT show up with a VOM testing at the pins.

A tube tester is handy. It allows one to develop a stock of good, trustworthy tubes such that when 'at work' one may simply substitute-and-test-later without agonizing. One also avoids cascade-effects, where a series of weak tubes give symptoms not attributable to any one (or two) tubes. A good example of such would be a multi-band radio that is perfectly fine on AM, but weak on SW, or silent on FM, if so-equipped.

So, Eric, out there on your island - if you want a tube tester, DO NOT go out there on eBay. DO go either to a trusted dealer - there are several - and expect to pay a premium for a good, clean, warranted device. OR, go to a trusted friend who is more in harm's way than you might be, and use him/her as a bird-dog for you. At Kutztown, there are never less than 30 - 50 tube testers on-offer, of which more than 80% of them are not worth the cost of plugging them in. Of the remaining 20% most of them are too much work to make reliable. Of those few remaining, they can be gems. But, I would guarantee that if one were to attend two sequential events, and have a budget of $200 or so (inclusive of shipping), one would wind up with a fully functional device with the correct literature to cover most of the tubes you will encounter in this hobby.

End Rant

Some other points:

a) An individual primarily working with instrument amplifiers as an example, will have a very limited universe of tubes to test. For that individual, a full-range tester will be heavily compromised due to its all-things-to-all-people requirement. That person needs a specialty tester. Those who routinely use, maybe, 10 kinds of tubes, but whose collection uses well over 200 kinds of tubes might be a bit hamstrung by a specialty tester.

b) There are those here that are genuinely dangerous, and should be strung up by their thumbs from the nearest lamppost for the advice they give. Have the wisdom to discern the issues involved.

c) And there are those here with specific prejudices, peculiarities and expectations - some more hostile than others. I more-or-less fit into this category at times. Same advice as above.

Peter Wieck
Melrose Park, PA