Tube Testers: Threat or Menace?
 

Reece recently gave this advice in another thread, "... still the best test for any tube is in the equipment in which it is designed to serve."

I've just spent a few days testing and retesting a few dozen used, NOS, modern, and vintage tubes with a newly-reconditioned Heathkit TT-1A and two emissions testers, and I can illustrate wisdom of Reece's statement. I have two 45's in a push-pull configuration in a 1931 radio that performs beautifully even though the tubes register nearly zero transconductance on the TT-1A. When I replace them with two spare tubes which (according to the tester) are much better, the radio's performance is, if anything, somewhat degraded, possibly because they're mismatched.

However, here are several reasons that you may want to buy a tube tester:

1. You can use it to confirm that your other tube tester is working.

2. You may be unable to test by switching tubes because you don't have access to known-good tubes or equipment that already uses the suspect tube.

3. As a learning tool, it can help the novice better appreciate how and why a tube operates.

4. It's really a fun toy to play with.

This was an eBay purchase that worked well for me. The wooden case disintegrated during shipping, but Heathkit produced a sturdy instrument, and it was well-constructed by the original owner. Putting this 15-pound beast back into operation was easy, thanks to Kent Nickerson and RDF Products who published excellent on-line guides for reconditioning the TT-1/TT-1A.

https://lh3.googleusercontent.com/-S...0TT-1%2520.JPG

Any other thoughts on the limitations or usefulness of tube testers?

Lots of good info there. As to the #2 point: for me, not having a big tube stock, it's helpful to be able to test a tube and get an idea if it could be bad before ordering a new one. I keep in mind that it may not be the problem, but if it test bad then the odds are in my favor and it's worth the gamble. I have a B&K 667, one of the last testers made, and it seems to work well and accurate.

Also, I believe if a heater is bad in a tube tester, it's for sure going to be bad in the tv or radio. I guess you could use a multimeter to check the resistance without a tester. But, it's a lot easier to stick it in a socket instead of trying to keep it from rolling while I try to get the probes on the right pins.

What I've been doing if I find a tube is weak, I mark it as such and set it aside. I think even weak tubes are worth keeping for the reasons above. After all they're not making many of them anymore; and who knows, someone may come up with a way to restore them in the future.

To keep a tube from rolling while trying to measure heater resistance, try plugging it into a socket you may have in the junkbox.

After checking about 60 tubes, all previously emissions-checked, I put one in the "bad tube" drawer and took 4 out of the "bad tube drawer" for possible future use. In the long run it may save me a few bucks, but mostly it's fun.

Also, if I ever want to sell any tubes, I can't promise they're good, but I can give test results. Still, the best recommendation for a tube would be, "I've tried in such-and-such radio, and it works."

Rolling tubes--I still don't have 4-, 5- pin tube sockets, but a few years ago I got a couple of extra meter probes and soldered alligator clips on them.

:lmao: :lmao: :lmao: :lmao:
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It took me a dam while, but I figured out how those dam smiley things work.....

Threat or Menace: No way, but I do feel that back-in-the-day they were a good sales tool!

They are more important now, than originally, as tube substitution is getting more difficult to do.

Tube testing just gives one a few more points of information on what may be wrong with a tube set.

I let the tube warm up for 5 minutes if it has been dormant for over 10 years. Then, I first test for shorts while gently thumping the tube, and if found, that ends the testing and the tube is rejected and I know to check the set more carefully than normal for signs of value change in resistors supplying this tube.

The tube is first checked on a transconductance checker. Assuming that it is not a diode, since the TC checker defaults to emission on those, it is then checked on an emissions checker. It then goes back in the set in the same socket with that information noted and will be used as an aid in diagnosing the problems. It may also tempt me to put that tube on my want list, which I always seem to forget to bring when I will be where tubes might be sold.

J.

I see them as a valuable service aid. Aside from HV rectifiers in TVs (which no tester comes close to giving a test under designed operational conditions), some oscillator tubes (the tester can tell how well a tube will amplify but not how well it will oscillate), and some tubes in TV horizontal deflection stages (those circuits can be REALLY finicky about tubes sometimes) it has been my experience that my tester is pretty darn accurate at pointing out tubes that are weak or bad.

Swapping the ones that test really bad for spares usually brings a stage, that has been otherwise recapped and gone through, back to life. If I test tubes before a recap and power up I usually put electrical tape on tubes that test in a range on my tester that I consider the marginal range as a mark so if the stage they are in seems to be not working well enough for my tastes or at all I notice the tube did not test well, and try a strong testing spare in that spot before diving into deeper passive component trouble shooting.

One case where a tube tester can give a semi-false condemnation of a tube is in the case of AA5 radio rectifiers. There are three heater terminals on those tubes one of which is a dial light tap which is tapped nearer to one of the other heater terminals so just enough power is bleed off to the light. If the section of the rectifier's heater that is in parallel with the filament is open then the tube will not light on some testers, and the tube can be considered to be bad by some schools of thought. However if one uses a beefier dial light in the radio and the previously mentioned problem is all that is wrong with the tube then the tube can still work in a radio. I recall reading an article that said that prior to WWII tubes with that defect would be routinely replaced, but once the war started and repair men could not order any more replacement tubes the dial light trick became standard operating procedure for nearly all repair men...Though some tried to fix open heaters through welding...

J., Tom: Thanks for the advice. I have immortalized you by printing your posts and adding them to my TT-1 operating manual.

I wonder if you can buy a new tube tester. I would say yes since so much audio equipment is still made. If they make the equipment then certainly they must make the test equipment. I just be it wont be a Hickok (my personal favorite)or something along those lines. Even if it is some Russian or Chinese job, it might be good if it were to cover all tubes from the old big pins through the compactron styles of the 60-70s. I always have to maintain two units to cover the bases.

As far as I know, the modern stuff is octal or miniature and that's it, but I may be wrong. As far as this thread, I suppose you can find deficiencies in anything, but by and large I say that a good tube tester is essential to anyone doing tech work on this kind of equipment.

I've never seen a new tube tester for sale. I doubt that there is enough demand for someone to start manufacturing them. There may be thousands who would want tube testing equipment but most of them are capable of renewing old models and that way they can chose among many varieties of equipment. Also, restoring an old set more satisfying than buying new.

I'm just thinking that if you worked for say Marshall amplification and you have all of these musicians wanting "matched sets" that there probably is something other than revamped older equipment involved. I'm sure some use it, because in many cases it is better. I don't think that even the more modern old stuff addresses mutual conductance. MBOS

Tube testers probably will make a comeback, if they haven't already. There are brand-new tube-type high-power home-theater amplifiers being offered for sale these days, and for good reason. Any real audio purist will tell you the only way to get real high fidelity sound from an audio system is by using tubes in the output stages. Solid-state amplifiers, even those with high-power output transistors, cannot hope to match the warm sound of audio processed using vacuum tubes. (Those of you who have old radios such as high-end Zeniths, et al. with push-pull or other types of hi-fi audio stages will know what I mean.) When those tubes short or become weak, there will have to be some way to test them (short of physically replacing the defective tube with a new one).

This is where tube testers come in. Until or unless high-power home-theater audio systems are again designed with transistors some years from now (however, I don't see that happening any time soon, if at all, for reasons I mentioned above), we will be seeing quite a few HT audio amps with vacuum-tube output stages. The tube tester used to ascertain the condition (cathode emission, etc.) of these tubes need not be anything fancy such as a mutual-conductance (Gm) tester or an in-circuit one like the old Hickoks, etc. I would think any type of emission tester would do just fine to test the bottles in these new home-theater amps, as long as the tubes are not so new as not to be listed on a recent ('60s-'80s) tube chart.

Sure, there are new, modern tube testers like the AT1000 for around $2,700.

http://www.amplitrex.com/about.html

or the EASY Tube-Tester V2.3 for $1280.

http://www.thebestamp.com/Testing_Eq...be-Tester2.php

I run into that problem even with old tubes. It's why, besides physical characteristics like not having a certain type socket, I have several testers. I would like to have one, but it just doesn't work that way.

And as far as new tubes and equipment go, I have nothing that tests something like the EL34 which has been common for years now. There should be a similar old school tube that one could use as a reference to set up an old tester.Thank God for the popularity of the 12AX7 and I believe the 6LG and maybe 6SN7. I can handle those.

My Eico 625 does 6CA7's, and a lot of other funky tubes too. Pretty sure it came out in the late 50's, so your tester much be a lot older I'm guessing? It does list a procedure for trying 'new' tubes, so it should be possible to figure out settings for one not listed. (pdf page 7, manual page 6)

http://diyaudioprojects.com/Testeq/E...ons-Manual.pdf


Perhaps the manual of your unit says something similar?