CDC 6600/Cyber 73 Memories - WAS: Harris H800 Computer

Paul Koning paulkoning at
Thu Apr 21 13:47:45 CDT 2016

> On Apr 21, 2016, at 2:04 PM, Rick Bensene <rickb at> wrote:
> ...
> The machine was an all-transistor design, based on the CDC 6600
> processor.  It was liquid cooled, and had a large cooler unit that sat
> with the machine that cooled the coolant (water) and circulated it
> through the chassis, venting  the heat (which was substantial) through a
> special venting system.  I remember the CDC Field guys talking about
> horror stories when there were leaks in the cooling system.  We never
> had any problems while I was there.


Nice memories, thanks for posting that.  I don't think there are any Cyber 70 (CDC 6000 series) systems still running, but there's one in emulation, running PLATO.  See  It even has emulated console tubes...

The machine itself was cooled with Freon (the non-PC flavor).  The chilled water you're referring to would take heat away from the Freon cooling system compressors (at the end of each of the CPU cabinets).

> One day I was at the console when one of the big high-voltage rectifier
> tubes that were in the console decided to short.
> I was watching one of the system monitor displays, and suddenly I saw
> the display collapse into a single very bright horizontal line.  I noted
> that the other display also did the same thing.   I also heard a funny
> noise that sounded kind of scary, so I started to push my wheeled chair
> away from the console, but not soon enough to avoid a shower of sparks
> and even some molten metal that spewed out from the console. 

Yikes.  I think the rectifiers were solid state.  But the deflection amplifiers used high power triodes (3CX100A5) as the final amplifier stage, running around 3 kV anode voltage.  If something goes wrong with those, sparks would definitely be a possibility.  And you'd expect to see a line (horizontal or vertical).


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