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In Reply to: RE: IIRC posted by DAK on June 12, 2015 at 21:20:54
Don't think the military would use so expensive tubes in a missile which is an expendable device. The addressing of cathode poisoning was key for the early ENIAC and Colossus computers , which although they were powered on 24/7, not all of the 1500 to 2500 tubes would be used. Many would be powered up but simply idling. There are many other 6SN7's which have the extra mica and support rods.Early versions had tremendous difficulty in both troubleshooting and tube failures.
Remember during WWII the military conducted many studies on tube life. They found that the more common the tube, the lower the failure rate, which is why the Red Base uses common types, not anything exotic. Cathode poisoning was not an issue as the tubes were limited in number and readily accessible.
True, long life tubes were important in Radar assemblies and stations which were also on 24/7.
100G capability was not really for missiles but more for US Navy ships which had to be able to endure shelling. You see this in 9 pin JAN tubes with their extra support rods, double thickness of mica, and extra "fingers" on the mica sheets.
The use of tubes drifted towards miniaturization, though. IIRC, 12AX7 gets introduced in 1954/1955. The 60's are dominated by the 9 pin miniatures. Even later, we get the nuvistors and then the truly miniature glass types which were directly soldered to the boards (VTV has an article about them too). IIRC they are still used on the Patriot anti missile missiles.
The current B 52's still use, IIRC, the 5R4WGB's, and their robust construction indicates the abuse they were intended to endure ( plus the high altitudes). The Russian 6C33 was found in that MG 21 which defected to Japan several decades ago. Highly immune to EMF, the US answer was better shielding.
Incidentally the HiPo 6S78 6SN7 that VTV tested came from my stocks
Edits: 06/13/15Follow Ups:
"Don't think the military would use so expensive tubes in a missile which is an expendable device. The addressing of cathode poisoning was key for the early ENIAC and Colossus computers , which although they were powered on 24/7, not all of the 1500 to 2500 tubes would be used. Many would be powered up but simply idling. There are many other 6SN7's which have the extra mica and support rods."
I am not so sure about that. In the late 40s and 50s during the height of the "red menace" the military was able to pretty much get anything they wanted. Defense spending went through the roof and all kinds of technology was being funded. So, I don't think the price of the tubes was any factor in its use in guided missles. But I am just glad that the 2 nations manage to not annihilate each other and we get to use some of the vacuum tube technology that was required for the times. cheers, Dak
Land based Radar sites and radio sites I can see the need for 10,000 hour tubes: but for a missile? Even for aircraft, 10,000 hours probably passes the mark for servicing.PS: At our local FAA radio repeater transmitter sites, the amps, which used KT-88's, were changed on a monthly basis, because it was cheaper than the manpower required to check out the tubes. 10,000 hours translates to 250 weeks. That's a long time for a missile or rocket to stay in flight, as well as aircraft.
Edits: 06/14/15
It would be great if anyone in the USAAF or SAC who worked with communications and/or missle or airplane avionics would let us know exactly what equipment the red base tubes were used in. But, still speculating, I would believe that the electronics for the missles in land based sites were always on as during that time the there were bombers circling the arctic circle carrying nuclear bombs 24/7. Crazy times! dak
I know they were used in Lockheed P2V Neptune autopilot servo motors. I've removed my share doing upgrades and conversions to firebombers. I kept what I needed and tossed the rest. This was about 1979-80. They also had 5881 and 5R4 as I remember.
In this case the 5692 was used in avionics where reliability and the ability to withstand severe vibration was a key requirement. While no one disputes that this tube was not designed for audio use, no one will hesitate to use it as an audio tube. I think the same can be said for the 6sn7wgt or 6sn7w which were also "industrial" versions of the 6sn7 family that are excellent for audio. cheers, Dak
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