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In Reply to: RE: FAA spec ? posted by Tweaker456 on March 22, 2014 at 12:23:33
IIRC, and I may be wrong, originally all the branches of the military promulgated their own specs. Army Air Force had slightly different specs for their acquisitions from the Navy, etc. Eventually they were all merged into JAN specs: Joint Army Navy. I believe FAA specs were incorporated into the JAN specs. I somehow remember them as being instituted in WWII however. It could be that the FAA had specialty requirements not covered by JAN specs.
Occasionally, I find chokes and transformers built with altitude ratings. These were obviously for air craft use although I do not know what danger there is for a potted transformer at altitude (maybe the potting might leak out ?). I do know the 5R4WGB rectifiers were originally designed for use on high altitude air craft like the B-52's, which is probably why they are built like a tank, to handle the extreme changes in pressure. And then there are the Bendix tubes with their ceramic spacers able to withstand the g forces of a ICBM....
Follow Ups:
Altitude ratings usually are an indication of resistance to HV arc over. Thin air at altitude is less resistant to ionization and arcing than denser air at sea level.
A great many tubes used in aviation (FAA) were actually employed in the ground based radios at centers, not to mention ground based radars.
Edits: 03/24/14 03/24/14
Is this arc-over between the pins or within the tube? Can't imagine that external pressure could effect internal workings of a tube, prior to extreme conditions.
Good to know. Thank you. Always puzzled me about those chokes and transformers as they didn't look very different from the non high altitude models.
What Steve said!
That's why the 5R4WGB has the "potato masher" base and unique shape - it was rated for use in excess of 40,000 feet - 45K IIRC. There were other parts certified for high altitude use as well.
I'm not disputing the air ionization factor, but one would think the octal bases of the potato mashers would show the ridges we find in larger power tubes like the KT-88's: providing a Longer pathway to prevent arcing over between the pins.
There may be more to the high altitude thing than we know. Then again, I never had an opportunity to take apart the potato masher base, so I have no idea what makes that base so unique other than its size.
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