[Amps] preserving tubes

[Bill Fuqua]

How thick are the walls on the cans?
Most ordinary cans will crush with a vacuum inside.
That is a differential pressure of 15 PSI.

73
Bill wa4lav
At 07:49 PM 10/4/2012 -0400, Roger (K8RI) wrote:
>On 10/4/2012 4:16 AM, ian at ifwtech.co.uk wrote:
>>If a tube has leakage to air, it is doomed anyhow, and storing it in a
>>vacuum can only delay the inevitable. Leakage will start right in
>>again when the tube is put into service.
>
>True, but:
>
>The military used to get 4CX150s in vacuum packed cans.
>Lets say a tube with metal to glass seals like the 4CX150, or PL172 has an 
>expected vacuum life of 15 years.  If you have a bunch of NOS (in the 
>cans) that are 30-40 years old when you open the can the tube  is starting 
>its life in the real world with an expected life of 15 years, while one 
>that was never in a can is most likely gassy without ever having been 
>used.  OTOH that gassy tube is highly unlikely to be at atmospheric 
>pressure inside, so if you place it in a hard vacuum the difference 
>between inside and out is not great and the tube is unlikely to ever 
>return to a high vacuum.  At least not within a practical time.
>IE the difference between 1 X 10^-5 and 1 X 10 ^-7 Toor or atmospheres is 
>miniscule compared to 15 psi (atmospheric pressure) and 1 X 10^-5 Toor.
>
>Too bad we didn't vacuum pack all those spare PL172s when they were new. 
>They'd be worth a small fortune now.
>
>
>73
>
>Roger (K8RI)
>
>
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