[GreenKeys] WWII-Era "Computers"

[Craig Sawyers]

> It had a TUBE "S.A.S" or stability augmentation system.
> First thing I was
> told during transition training to this huge monster
> was...don't ever turn
> that on !
>
> I didn't :>)

The trick was - don't ever turn it off.  When Tommy Flowers came up with
idea of Colossus to break the Lorenz messages, his standing instruction was
never to turn them off.  Tube reliability is all to do with the thermal
shock of turning them on.  Don't turn them off, and they have a typical life
of 10,000 hours (over a year at 24/7).

In the Colossus rebuild, with 40 original WWII valves in its complement of
2000, it isn't switched on 24/7 (it consumes 5kW!), but the heaters are
brought up slowly on a motorised variac, and the HT is only switched on when
the machine is being demonstrated to visitors.  Yesterday, over 800 visitors
looked at Colossus.

Craig