[time-nuts] Making a 10811 better

Jim Lux jimlux at earthlink.net
Tue Sep 20 21:38:22 UTC 2011

On 9/20/11 12:46 PM, J. Forster wrote:
> Likely one of the Freons (TM) or Sulphur Hexafluoride.
> Tektronix used a Freon in their 40 KV High Voltage probes. The Vapor
> pressure of some of those compounds is low at 70F, but they do have to be
> sealed.
> Unfortunately, virtually all Freon useage has been banned by the EPA (they
> are said to be "greenhouse gases") and the stuff in now almost unobtanium.
> -John
> ===============
>> Long ago and far away, I recall a friend using a gas that had its
>> liquid/gaseous transition near room temperature and was inert (not an
>> inert gas) to pressurize a vessel having high impedance circuits in it.
>> I'm darned if I can remember what it was. Available in so-called "lab
>> bottles" ie not monster cylinders.
>> Would have to be sealed, though.
>> Don

All manner of refrigerants fit the bill. some form of halogenated 
hydrocarbon for the most part, and while regulated, they're still 
available.  Just not dirt cheap.

SF6 fluctuates widely in price.  It was really, really expensive 10-15 
years ago (as flourination plants were used to make non CFC 
refrigerants) but has come down a lot.

In lecture bottles (2 SCF) all gases cost about the same $100

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