Hi All:

I use tube testers a lot these days testing tubes for my radio restorations as well as selling tubes on ebay. I have a B&K 667 Emissions tester and test all tubes before selling or installing them. Lately I've had a few issues with Mutual Conductance (MC) tube tester owners buying my tubes and telling me they are weak. Argh So I have been considering getting a MC tester but I want to be sure the increase in cost is worth it... it must make a meaningful difference towards insuring the quality of tubes I use and sell.

I'm looking for insights here to help me make a smart buying decision (or not buying), I look forward to everyone's comments.

Thanks! Tom

Well, I do find the relative numbers values from my TV-7 tester are well received by buyers and no complaints yet, although I do not sell that many tubes these days. I am not gonna bother selling 3-5$ common tubes with all the competition and why bother with the hassle for a fiver. I also have an emissions tester due to the fact that alot of late model tubes are not compatible with the mil. tester. I would say that I have had reasonable results with the emission tester as compared to the TV-7 but the tests are not exactly comparable. And the emission set has a more sensitive leakage test. Just the other day I had a tube that was fine for "shorts" and emission but weakish leakage indications occured and it turned out the leakage was responsible for a dead FM section. With the mutual cond. tests you can supply your buyer with hard numbers and so with that perhaps if they think there is a problem they maybe defer to your "fancy tests".

I think it is a dollars and cents question. How many tubes are you selling and what are you selling them for. If they are low cost low demand tubes, then you state the results from your current tester and sell the tube as is. If they are more desirable tubes, and more costly types, then there is value to having more validated GM results on a calibrated or validated tester. There is a wide window on test results between tube testers, and there is often no guarantee that a buyer will get similar results to yours.

I probably will get a lot of feedback on this one, put for the most part if you buy something like a Hickok tester, most of them work the on the same principle and I do not see any need to get anything fancy (i.e. spend large bucks). There are difference between the older models and newer models, such as signal levels, which can have an adverse effect on test results of say a 12AX7 and a 5V signal level. You also do not want to sell a bad tube. Gas tests vary by tester, the 580 series is very sensitive, other Hickok's less so. But I do not see that you will get any better results with a military model vs. a more mundane model. If you can pick up a higher end model for cheap then go for it. Certainly, you will get a higher price for your tubes and not have to deal with returns or negative feedback.

B&K made a number of Gm models which use the standard Hickok circuit and work fine. They were however designed for TV servicemen and may not test older or specialized types. But then the 667 was for TV work too.

I have a B&K 650 mutual conductance tester which tests a LOT of tubes, but it doesn't test really old tubes.

Readings will vary when the same tube is tested on different mutual conductance tube testers, mostly due to various testers using different operating parameters when testing a tube.

I have relied on tests from my Triplett 3444 and Hickok 752A testers when selling tubes, and have had only one complaint about the tube that I sold. I refunded the $$ to prevent any hassle.
Buyer said that his tester (a cheapie emission parameters. ion tester) said that the 83 I sold him was weak. Easier to refund than argue. Otherwise, I've had no complaints. Both testers give accurate readings, though the readings are different - different test parameters. It IS a matter of money. Are you going to sell enough tubes that the MC tester will 'pay' its way? That is a valid question.

Gene

The problem is, even if you bought a mutual conductance tube tester, your customers would just amp it up higher. Your tester is a lower model on the food chain than their tester, yours wasn't calibrated by the same "guru" who calibrated theirs, etc., etc.

All testers are going to have some variations in the test results, and the absolute value onto itself is not that meaningful unless it is below the min value. If someone has a 20% lower reading then your test results, it really doesn't mean much, especially because the vast majority of tube testers give a result under one set of operating vales and they are not precision instruments. But I still believe that a buyer will have a lot more "comfort level" if you have mutual conductance values on something like a Triplett, Hickok tester, Amplitrex or similar. Those that are going to complain, it doesn't matter what you do, it isn't good enough or their running a con game and want to squeeze a little more out of you. So with all that, I would expected that you would get a better return and have less problems with a mutual conductance tube tester, it is a question of value. You also disclose that your results maybe different, tubes are sold as is.

This is all really GOOD information to help me decide on whether to get a MC tube tester. Let me ask, if I do try to get one are there any brands I should avoid? I am familiar with B&K... I like the 747... is that a good choice other than not testing the really old tubes?

Yes. The B model has a panel-mounted circuit breaker instead of an internal fuse. It does have the limitation, like all B&Ks, of only four fixed bias levels.

This thread may help:

viewtopic.php?f=8&t=193114

Hope so. Best regards ,

Larry

Wouldn't surprise me if these were simply a bunch of fly-by-nights trying to get something for nothing. It would be a surprise these days if you didn't encounter buyers like that, especially where tubes are concerned.

Larry

Does the 747 test mutual conductance for the tubes in the general purpose sockets or is it straight emissions? I saw this noted for the 707 elsewhere.

Again, just wondering if the B&K will cover most of what I will encounter with only 4 bias levels. Is this a serious limitation that will make a purchase regrettable? I may want to determine test parameters for tubes not listed. If it is not too limiting and it was in good shape what would be a fair price?

In your place, I'd get as versatile a tester as I could justify owning, whether I was selling tubes or not. No single tester covers ALL the bases, but some cover more than others.

The major trouble you face may not be in the type of tester you get, but the nature of your clientele. You could get the sexiest tester in the galaxy and still fail to please some of them, especially if you're servicing the Audiophile or the twang-and-bang crowd.

Don't know about the 747; never touched one. The 707 is certainly a hybrid, but it's also durable; trouble is, it won't handle the older types. I like my Weston 982 very much, but trouble with it is, it won't handle a lot of the newer types, including the novars and compactrons. You'll face a compromise of some sort, whatever you get.

Good hunting,

Larry

The 747 will test Gm for all tubes.

I've been looking at a few B&K 747 (and others) on ebay... can you tell me where the panel-mounted breaker would be if it has one?

The B&K 747 Breaker as shown. Please note as Alan mentioned this tester has only 4 bias settings and does not give direct readings in micomhos, which is number that tube buyers are more familiar with. These are reasonably decent for Good/Bad, but not much more than that as outlined at alltubetester site, so probably worth looking at http://www.alltubetesters.com/articles/tester_guide.htm or http://tone-lizard.com/Tube_Testers.html for comparison of models/features. I haven't used the B&K 747, it maybe better than what you have, but may not give you the results that buyers are looking for.

If your electronically capable, then building something like the uTracer may be cost effective and give excellent results. http://www.dos4ever.com/uTracer3/uTracer3.html "I have used the uTracer for a while now and it gives the exact same measurements as the AVO Mk III, Mk IV, CT160, CT160A and VCM163 and also the Taylor 45D and 45D2 plus the much more expensive RoeTest, I own all of these so I have been able to compare their measurements on many different valves." It will probably be my next build project despite have a number of other excellent tube testers.

WOW! I had no idea something like that existed! I am very interested....

Yes, the uTracer sounds really cool and I will give it a serious look... I can built these things.