[Milsurplus] How Much Vacuum in "Vacuum Tubes?"

[Gregory W. Moore]

GE Bob,

Thanks for crunching the numbers for me, I just didn't have the figures 
handy, nor bothered to figure the pressures out
when doing the email... the 47 torr is a neat piece of data, and of 
course refers to the "Armstrong Line" of 63,000 feet,
where it simply isn't a good idea not to have a suit ;-).  I for one 
would have liked to see the CRT working without an
envelope, but unfortunately, my chamber runs were strictly no frills, 
but I did get to have the great thought about the
aforementioned 47 tor during my pressure suit indoctrination runs....the 
people who ran the chamber always thoughtfully
put a beaker of good old water in the chamber where one could see it 
plainly, and the results of the vapor, boiling, and splashing
made you really appreciate that you were enclosed in, basically, a 
35,000 ft pure O2 environment.  Thanks much Dave Clark
for your original AN/P22S-2 and the various modern derivatives thereof.  
(Also for your fine headsets). 

Anyhow, I am filing this message where I can refer to it, and even tho 
retired disabled, ( powers that be take dim views of
those with closed head injuries and venous stasis retinopathy in their 
left eyes sitting in the pointy end of stuff which defies
gravity ;-)  I can prove that an Aeronautical engineer who also happens 
to be a airplane driver, with the fun of flying certain pieces of  
military ironmongery to substantial heights actually knows what he is 
talking about..
again 73
de Greg


Bob Camp wrote:

> Hi
>
> Very interesting stuff about the hard suit's origin. I had never  
> heard that part of the story before.
>
> A few numbers:
>
> Sea level pressure 760 torr
>
> Pressure at 25,000 feet = 282 torr
>
> Pressure at 30,000 feet = 225 torr
>
> Water boils at body temperature at a pressure of 47 torr (wonderful  
> piece of data)
>
> Vapor pressure of Mercury at room temperature (mercury vapor  
> rectifier) 1.7x10-3 torr
>
> Pressure at 1,000 Km = 10-10 torr
>
> Pressure at 400 Km = 10 -13 torr
>
> The easy way to measure vacuum is to set up a diode or triode in the  
> environment and measure it's leakage. When used that way the tube is  
> called a vac-ion gauge. Regardless of the name, it's still a tube,  
> filament and all.
>
> CRT's came into being long before high vacuum was a reality. The  
> electron beam looks a lot like a light saber flying around under  
> magical control. It's a very cool demo.
>
> So much fun ...
>
> Bob
>
>
>
>
>
> On Apr 1, 2007, at 3:39 PM, Gregory W. Moore wrote:
>
>> GA, All
>>
>> While I have never made a "circuit usable" vacuum tube from  scratch, 
>> I did, in the early 1970's make a triode
>> out of parts salvaged from several different tubes, blowing the  
>> glass envelope myself, and using the services of
>> a CRT rebuild house to pull the vacuum on said tube.  Now, the tube  
>> did not have a getter, but I managed
>> to make a octal base which was similar to another triode ( now that  
>> I'm 59 I forget just what I used) but It
>> tested "good" in a transconductance tester, and probably would have  
>> worked in a circuit, except that the
>> process of testing, I managed to burn the filament out testing  
>> higher filament voltages.  SO, I would imagine
>> the concept would have been viable back in the day, I wish I could  
>> have used the homemade tube in an
>> actual application to see if the gain, and current curves would  have 
>> matched a commercial manufactured
>> tube.
>
>
>


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