[Amps] preserving tubes

[Roger (K8RI)]

On 10/4/2012 7:49 PM, 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

That should have been 4X150, not 4CX.  Both the 4X150 and PL-172 had 
metal to glass seals and tended to get gassy just setting on the shelf.
The 8295A version of the PL172 used a ceramic to metal seal and were not 
noted for having the tendency to go gassy.

73

Roger (K8RI)

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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