JAN TESTED TUBES
Military tested tubes are strange items in the world of HiFi. As if they do not belong there, because whatever the army is doing, has nothing to do with listening to music. In this small article I will try to describe the advantage of JAN TESTED tubes. Perhaps I will convince the reader, but this will not convince the "crowd" because once something is believed, or not believed, it is supposed to be that way and not another way. So use this knowledge in your advantage when you check those uninteresting products, that not everybody is shouting about. It is just this what JAN TESTED tubes are. These provide higher reliability, as this was the intention of JAN TESTING.
6922 / Philips / JAN TESTED / Order Number: 114-096-33
What is reliability? This is a much misused word. Do not confuse that with quality. Please let me explain.
Quality means something has much better properties than average. Quality has always been hard to measure, like how can you measure the quality of sound.
Reliability is not quality. A low quality product can have high reliability. Or vice versa. Like hammer can be a very low quality tool, but you can use a hammer for 50 years, and have no defect. Or a high quality product can have low reliability. Low reliability is not so much the result of using low quality products, but more the result of bad work during manufacturing.
Uptesting: Increasing the reliability or quality of a product, AFTER r production. This is done by screening out the unwanted products. Like you can increase the precision of a test instrument, just by screen out the ones with lower precision. So you change nothing to the productiom process, but still you increased quality that way. This is called uptesting. A word to remember.
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Let me give you an example, I was given myself in a JAN Training at Hewlett Packard. Suppose you need to purchase water glasses for use in airplanes. You want only such that do not break uf they fall off the airplane table. Take standard glasses, and some will break, some will not. You want to buy 100.000 of those, with a low chance to break. How will you verify that? Will you buy 100.000 glasses, drop them all one by one, and only use those that survive? Probably not! You will do sample testing on glasses of different vendors. The brand that performs best, is your favorite. Also you don't like to test samples yourself. Let the vendor do this, and agree he must document it.
Now look at just one such a glass from an approved lot. There is high belief, if you drop it from 50cm, it will not break. Though this is not guaranteed, it's just the chance on breakage that is lower. From the test results you had before, this chance can even be seen, as you know for instance it was 1:15 for the best vendor, and 1:4 for the worst vendor. But you want more. You want better than 1:25.
Now that becomes difficult, such glasses can not be produced. So now comes JAN TESTING. You describe all vendors how to do this testing. Each time he makes a lot of 1000 glasses, he must take 100 pieces out. These 100 he must drop from 1 meter! This is definitely too high, but some will still survive, and it's just THIS that you want to know. You will agree, if glasses from Vendor A have a 60% change on breakage, and Vendor B only 15%, you want to glasses from vendor B. And no, you don't want to have those that survived, also not from vendor B, as they may cracks now. So the lot which was used for testing, the factory can sell it on Ebay, or recycle the glass. The remaining lot (of 90%) these are the good ones! If the factory now gets 50% more for those, it pays off to destroy some 10% for testing. This is how JAN TESTING works.
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Reliability means the PROBABILITY a product keeps working during a SPECIFIED period of time. Now isn't that what we all expect, and this a simple engineering parameter, called reliability. When it's puts into a number, it's expressed as MTBF (Mean Time Between Failures) So same as weight is specified in kilogram, reliability is expressed in MTBF.
With that number, engineers can calculate the chance on a product error during a specified number of use hours. With tubes, reliability is well recognized, as used tubes no matter how fine they test, have much less value as unused tubes. Prices are are also related to a specific brand, type, construction or date code. That is, because some people seem to know how a lot about this, and others no so much at all. Some believe Gurus, and some others only what they can verify. It is just here where JAN TESTING is a great a help.
With tubes, JAN TESTING exposes the tubes to an overload situation, above the datasheet limits. It is obvious this creates some defective percentage within some time. From a lot of 10.000 tubes 100 are taken, and these are overheated slightly, and run for 1000 hours that way. All you want now, is a pre defined survival percentage for this lot. It is obvious, you want only those 9900 tubes that are not tested by overloading them, but if the survival rate of those 100 tested tubes was good, you have better belief in this lot.
In a practical situation, this survival rate is defined, and also the overload situation is defined and the number of hours. The result of this, after some difficult math, is a parameter, called MTBF. (Mean Time Between Failures). Once you have the MTBF, you can use that number to do any calculation. Like what is the defect rate in percent, after 9000 hours, at 70% of maximum dissipation. There are formulas and tables for this in the military handbook.
Can you repeat those calculations? Unfortunately not. With JAN TESTED tubes the MTFB is known to the buyer, but it is not communicated externally. All we have is the code numbers on the box. Sure is however, these have a higher reliability than commercial tubes, and lots that did not pass, were sold normally as commercial tubes.
JAN means: Joint-Army-Navy. The army does not do the testing themself. Tests are done by tube manufacturers in house, and must be documented. The lots must be numbered, lot numbers on the boxes, and army inspectors will visit the production sites for inspections. So you always will see a lot number, the manufacturer code, the date code, and the actual test specification code. This leads a government inspector always to the original factory documentation for any failed tube.
So JAN doesn't say anything about initial values like transconductance or anything like that. For that there is a datasheet. JAN means the tube has a higher change to KEEP the datasheet values during it's specified lifetime. It is recognized this chance is never 100%, and the number MTBF can be used with formulas and tables, to make a forecast about this chance. I would say for buyers of NOS tubes it is just a good thought, knowing this chance is HIGHER with JAN tubes as with none JAN tubes.
Done so ever since, and JAN testing is still used for semiconductors as well.
You see, the good part is, the crowd doesn't know and doesn't understand this. So take your advantage :)