> On Jun 7, 2018, at 2:50 AM, Rick Bensene via cctalk <cctalk@classiccmp.org>
> wrote:
>
> ...
>
> Believe me, the console did spit out a lot of sparks and little blobs of
> molten metal, along with quite a bit of smoke. I still have a small
> scar on my left leg where one of the little blobs of metal burned me
> after burning through the material of my slacks.
I definitely believe that. There's quite a lot of stored energy in that
device: 2 kV power supplies with a pair of 4 uF filter capacitors, if things
short out you will definitely get some excitement.
> I remember keenly one of the CDC field guys saying that one of the big
> driver tubes had shorted. There were quite a slew of other parts
> (including some smaller vacuum tubes) that ended up being replaced, as
> well as the left CRT tube which had a phosphor burn right in the center.
> ...
>
> Whatever the cause of the failure, it was something that surprised the
> CDC guys. Maybe the shorted tube was an artifact of the failure, and
> not the cause...hard to remember exactly. But, I do know that two of
> those big ceramic and metal tubes were replaced, as well as the left
> CRT, and a whole slew of other parts. And I do clearly remember them
> saying that the driver tubes had to be replaced in pairs.
If the final drive tube shorts plate to grid, you'd get 2 kV working its way
back into the previous stage. Those tubes are only rated for a few hundred
volts on the plate. Not to mention that 2 kV feeding back into the previous
stage power supply would be a problem also.
As for replacing in pairs, it's a differential signal path and it would not be
surprising if they required matched pairs.
paul
