7 Jun
2018
7 Jun
'18
6:19 a.m.
On Jun 7, 2018, at 2:50 AM, Rick Bensene via cctalk
<cctalk at 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