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I have a Sylvania 6cg7 labled JAN. It has green lettering. I know its designated for the military. Are these hand selected tubes?
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Made for the forces . Some may claim JAN branded tubes are built to better standards , which is unlikely
Al
WAF just not there I'm afraid...
Hi, I don't know what you mean by "hand selected" but take your tube. The 6cg7 was probably not used in "harsh environmental conditions" so it was probably procured for more mundane use like a PA system or the like. But even so since it was government military contracted it still had to go thru a burn in period and tube testing for matched sections and specified output. I am pretty sure there was a technician involved in that. Not knowing what other aspects of the military specs were we can only guess. Other types of testing involved shock and vibration. On/off cycles, atmospheric pressure and temperature and specified life span. happy holidays, Dak
If you have ever sat upon a Jan C-140 crapper, you might not be so high on military testing standards.
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The can on a C-140 transport. It was supposed to cost in 6 figures for each one.
Hey, do you know how much they had to pay people to crap in that head to get the MTBF numbers?
You got it...Mili-spec, but not hand selected. Just needs to meet military specifications. Joint Army Navy
They may be selected for parameters other than audio quality, such as shock resistance, temperature extremes, etc.
JAN tubes are generally very reliable.
As long as it is clear that JAN tubes are not hand selected from a larger population of tubes...really, they are not selected at all, rather manufactured to contractually published military specifications.
Your assessment is not really accurate. Every JAN tube was "expected to be" humanly tested for it's high grade, military usage parameters. It is undoubtedly true that a human being controlled the testing, hand-changed the tested tubes and monitored the actual testing procedures.
When you can find the info, read the Western Electric testing and burn-in techniques; allegedly achieved for long, reliable life. Similar techniques were supposedly utilized by all USA tube manufacturers. Those older, brown or very yellowed, circa WWII or Korean War era tube boxes contain well broken-in and high reliability tested tubes inside. Even the sixties, Vietnam conflict era tubes were manually tested and chosen for a reliable, rugged and long life...
You may think as you wish.
"Every JAN tube was "expected to be" humanly tested for it's high grade"
Well, the key word of "expected" allows one to fit this statement into a variety of positions. Still, the assertion that every JAN tube was tested by the tube manufacturer to ensure they met all the parameters of the military spec, for all the years that JAN tubes were issued (circa 1940's to circa 1980's) is simply not true.
My cousin worked for Sylvania in the 1950's. He claimed every tube would sit in an activation and stabilization rack as part of QC. This is very different from the QC sampling of tubes for the full array of tests - micro-phonics, balanced triodes (when applicable), and other aspects of the mili-spec.
I can recall my military buddies running a burn-in of hundreds of tubes prior to using them in military gear. Why would that be necessary if all tubes were hand selected to ensure 100% spec?
Most tubes would pass the burn-in, but keep in mind that the burn did not test for all required specs of a given tube. Also, many tubes that failed burn in allegedly circulated into the commercial tube markets and ended up in computers, broadcast stations, home amplifiers etc.
At Sylvania, if a tube failed the activation and stabilization testing, the tubes were accounted for and sent to a massive crushing machine - not unlike a junkyard crushing machine to ensure the tubes with the Sylvania name did not get into circulation.
The Sylvania Crush Machine
Edits: 12/21/15
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