local demolition of SAGE building

[William Donzelli]

> Further like all thermally
> affected things temperature cycleing ws not only a filament problem but tube 
> seals (glass to metal) and element movement is problematic.

Yes, thermal cycles are an issue, but only if the number of cycles gets
really excessive. The minis used in computers, even in large numbers, just
do not get that hot (provided they are cooled properly, of course).

Keep in mind the tube guys had lots of practice with minis in thermal
cycle in the late 1940s with the complex and dense aircraft radars (120 F
on the ground to below freezing in a matter of minutes for something like
an /APQ-35). Even some of the radios packed a huge number of tubes for
such a small box (thinking /ARC-27), yet thermal cycling was not so much
an issue.

>  Many high gain 
> tubes have remarkably close spacing of the elments particulary cathode to 
> grid1.

Most computer tubes were 12AX7oids, occaisonally with a 6BA6oid. The
spacings were not very critical in these relatively low gain
devices. The high gain tubes generally were avoided (perhaps for this
reason). I am not home right now, but when I do, I will see if any maker
produced any high gain computer rated tubes.

>  Another phenomenum was tubes have materials to grab gasses and ions
> in them that only work well when hot.

As far as I know (and I will check with the tube gurus), no computer tubes
used these materials. Eimac was a champion of tantalum plates, the metal
that swallows up the crap when hot. Barium getters are not an issue.

> The smaller mini and submini tubes
> were only somewhat better

A magnitude better. Probably a couple magnitudes better for subminis. The
damn things just do not die (unless abused).

> There were even special tubes developed that would better withstand being 
> at cutoff for extended periods without losing emission.

Yes, these are the computer rated minis I have been mentioning. As far as
I know, all commercial and military post-1950 computers used them in place
of regular types. I keep every one I find, in hopes I will need them some
day for a 709 or something. At this point I probably could tube up a 709,
actually...

William Donzelli
aw288 at osfn.org