1966 Mag: Build NE-2 Neon Bulb Computer - scan available

[CRC]

On Thu, 26 Jul 2007 21:50:07 -0700,  "Chuck Guzis" <cclist at sydex.com>  
wrote:

> On 26 Jul 2007 at 21:39, dwight elvey wrote:
>
>> Hi
>> I have soem tubes made in the 1920's that still have a
>> good vacuum. How much longer should I wait.
>> Dwight
>
> Isn't that the whole idea behind a getter?

Activated getter works on active gasses (and some of the heavier  
inert ones also) up to the point where the activated surface becomes  
saturated. In a well sealed tube, that can be a substantial time.  
However, it does not work with helium. Helium abhors a vacuum and  
will attempt to equilibrate its partial pressure inside the tube with  
that outside - glass  and getter be damned. Same goes for HeNe lasers  
- the helium inside makes for the outside world and the laser goes  
south. I've been keeping a pair of HP Interferometers going for years  
by occasionally putting them in pure He for several weeks, all the  
time measuring the output and waiting for it to come back to spec. If  
you have an old, well-sealed tube that has gone gassy due to helium,  
you can rescue it by putting it in a high vacuum for a couple of  
months...

	CRC