|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
80.133.126.63
In Reply to: RE: most intresting tube posted by dadbar on July 21, 2017 at 07:24:59
?? what does make the difference between the bulbs inner vacuum in 50,000 or 5,000 altitude. can anyone explain please?
N.
"How the fuck did our oil come under their sand?"
Follow Ups:
The vacuum level is determined by the pressure differential between the evacuated volume and the surrounding atmosphere, therefore, tubes used at high altitude would require a higher vacuum than tubes designed for sea level application.
sorry - i am afraid you are wrong. the inner abolute pressure (the quality of the vacuum) in the glas is always the same at any altitude! the bulb is sealed, so the vacuum inside does not notice what happens outside the bulb. not even on the moon...
N.
"How the fuck did our oil come under their sand?"
This link may ex[lain it-
"This link may ex[lain it-http://anver.com/vacuum-lifters/atmospheric-pressure/ "
No, that is a completely different issue. The page you linked to is on vacuum lifters, namely using something like vacuum cups to lift a load. The point they are talking about there is concerned with the fact that if the air pressure is less, then even with a perfect vacuum in the lifting cup, the weight that it will be able to lift is reduced in proportion to the reduction in ambient air pressure. I think the way they express it on that page is actually a bit misleading, since they seem to be measuring the "degree of vacuum" in terms of the lifting power at a given altitude relative to what it would have been at sea level, given an ideal vacuum inside the lifting cup in each case. Anyway, that is their problem, and it has no bearing at all on how vacuum tubes operate at altitude.
The situation with a vacuum tube is completely different. As nunki says, it doesn't matter whether the air pressure on the outside of the vacuum tube is normal sea-level pressure, reduced pressure at 50,000ft, or the vacuum of outer space, as far as the degree of vacuum inside the tube is concerned.
My suggestion, as I said before, is that maybe it is something to do with the thermal dissipation behaviour. The way in which heat removal by convection works will presumably be significantly different if the ambient air is rarified, such as it would be at 50,000ft, and that might conceivably make enough difference to matter.
I suppose another possibility is that in sufficiently rarefied air, the electrical insulation requirements outside the tube may alter (increased likelihood of arcing or discharges between nearby pins with a large potential difference between them). This might imply different design criteria, perhaps.
Thinking about it, I think I'd probably put my money on the arcing problem as the most likely explanation.
Chris
Edits: 07/24/17
The ignition systems in aircraft are pressurized. Well, maybe not all, but if you take a look at stuff like the R3350, R2800, V-1650, V1710, the Napier Sabre and others, the HV stuff is all fed from a compressor so as to preserve the ignition performance at high altitude.
Now with octal tube sockets, an octal is an octal, so consider the insulating material. The vacuum level in all of these is high, and absolutely independent of outside pressure. Not sure how far you'd have to go to find a harder vacuum than what is inside...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
"Now with octal tube sockets, an octal is an octal, so consider the insulating material. The vacuum level in all of these is high, and absolutely independent of outside pressure. Not sure how far you'd have to go to find a harder vacuum than what is inside...:)"
Indeed, but its what's going on outside, not inside, the tube that matters. A quick googling of Paschen's law and related articles suggests that at 50,000ft, where air pressure is maybe about 12% of sea level, the voltage needed to cause an arcing breakdown across a given air gap is roughly one tenth of what it is at sea level. Maybe that could be quite significant, and might perhaps might impact how the tube and the base is designed.
Chris
Sorry, try this link. It covers altitude as well as almost everything you ever wanted to know about vacuum tubes. Hope you have a lot of time on your hands :)
"?? what does make the difference between the bulbs inner vacuum in 50,000 or 5,000 altitude. can anyone explain please?"
Maybe something to do with heat dissipation, and the difference in air convection at low pressure vs normal pressure?
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: