OK, I will go straight at this one:
1. Tube testers are useful if:
a) One handles either a lot of tubes, or a lot of equipment that depends on tubes.
b) One understands what they can, and especially what they cannot do.
c) The tester itself is fully checked out and is operating as it should.
2. There are two basic classes of tube testers:
a) A simple emissions-tester. This, in essence, simply tests for conduction from the cathode to the plate.
b) A GM Tester that also tests the grid, and tests the tube at a fixed bias.
3. Within each class of tester, there are sub-classes which actually separate 'good' testers from 'not so good' testers:
a) A simple emissions tester that also tests (properly) for shorts and gas can be very useful. Shorts must be tested with a *HOT* tube, as many types of short do not show up with a cold tube. and with that group, some do not show up until the tube has been heated a while. So, a tester that can also sustain the filament load and plate voltage for more than a few seconds is worthwhile.
b) A GM tester that does the same is useful. But, one that also will allow measurements of filament current, plate current, and will allow variable bias and/or an external bias source now has the capacity to do matching. Very, very few testers have these specific capacities. Those that do tend to be stupidly expensive.
4. Why own a tube tester:
a) A power tube that flashes over, or shorts in use can cause all sorts of spectacular artifacts. Similarly, a rectifier tube. Small signal tubes less so, but still can have unfortunate effects should they short in use. So, if one has a piece of tube-based equipment, AND
a tester that does shorts and gas, one has the ability to screen the tubes to some degree before applying power to the device.
b) If one is into audio at a serious level, it can be quite useful to determine if any tubes, especially power and rectifier tubes, are marginal. And similarly small-signal tubes are doing as they should. This settles many otherwise indeterminate questions - is it the device or the tube(s)?
a) I keep several dozen tube-based radios from 1919 through 1963. I have several thousand tubes stored away. With all that, my simple Simpson emissions-tester is sufficient for 90+ % of what I do with tubes, as it does an excellent job with shorts and gas, and can sit with a 6550 in the socket for as long as an hour and not overheat. What it will NOT tell me is anything other than gross differences in quality between any two tubes. http://radiolaguy.com/images/equipment/Simpson_555-p.jpg
b) I also keep a Hickok 539B, fully calibrated and obtained legitimately from GE Re-Entry Systems in Philadelphia some years ago. This tester has all those obscure capacities and can match tubes effectively. It can also determine quality differences between tubes effectively enough that a decision to scrap or continue-in-service may be made on a sound basis. I use it about 10% of the time I am screening tubes. http://jimmyauw.com/wp-content/uploads/2010/01/hickok-539b.jpg
I deal in more than a few radios that use both rare and exotic tubes such that junking a tube merely because it is suspect is not an option. Eye tubes, and some power output tubes fall into that class, as well as some of the pre-octal tubes that were never made in vast quantities. Check out a 6T5 some day if you want a perfect example. So, to that end, a tube tester is a useful tool, mine have paid for themselves many times over. And, the first blown output or power transformer from a slagged tube (heat-related short) handles any other doubts one might have.
a) Any tester contemplated *MUST* test effectively for shorts and gas. Otherwise, it is pretty useless for reliable screening other than go/no-go - and most of the time that can be done with a VOM.
b) Unless one is heavily into tubes and understands the multiplicity of types and applications, an expensive GM-type tester is probably not a good investment.
c) Military testers (The Hickok-pattern TV7 being a prized example) were designed for a very specific purpose under very specific conditions and generally not much more useful than an emissions tester in the world we inhabit. Yes, they will differentiate to a much finer degree tube *quality* (term-of-art meaning how close to new-spec. any given tube might be, not how well it is made). But it is not useful for matching purposes and cannot be made to be so. So, unless one is committed to a lab-grade unit, a higher-end emissions-tester (REPEAT: SHORTS AND GAS) will be sufficient.
d) Unless one purchases a 'new' computerized tester (and, yes, those are still being made with quite a few options), the typical tester one sees on eBay is starting at 50 years old, and counting. Well made testers, like well made anything elses, will stand the test of time and are readily maintainable. But, unless one gets a tester from a reliable source and/or REALLY understands complex troubleshooting, https://i.imgur.com/XWylh.jpg?1
this is not an exercise for the faint-hearted.
I paid $15 + about 4 hours for my Simpson.
I paid $100 + about 8 hours for my Hickok.
Purchase ONLY from reliable instrument makers. And there is a truism amongst tester users:
Accurate/Supreme/ HiTech et.al. aren't.
Reliable brands (most of the time) are: Hickok, Simpson, Heath, Eico, Jackson and a few others are good points of departure.
e) Equally as important as any given tube tester is the paper that comes with it. Which must have, but not be limited to: A complete owner/shop manual. Obsolete tube data. Updates at least into the 1980s, if not beyond. Data sheets for WE (Western-Electric) pattern tubes. Sockets or adapters for 4-pin through Nuvistor tubes. And Euro-pattern tubes if one is into that as well.
Of the brands named above, all of this is available for all of them in the after-market.
Last edited by Peter W. on Wed Jan 04, 2017 2:31 pm; edited 2 times in total