6 Apr
2022
6 Apr
'22
6:22 p.m.
On Apr 2, 2022, at 6:27 AM, Liam Proven via cctalk
<cctalk at classiccmp.org> wrote:
On Sat, 2 Apr 2022 at 00:34, Bill Gunshannon via cctalk
<cctalk at classiccmp.org> wrote:
But that true for earlier machines, too. Replacing broken transistors requires having
replacement transistors suitable for the circuit in question. For a 1960s era machine
that may be quite hard; while transistors are easy to find, transistors with suitable
characteristics might not be. And what are they? I'd love to know what the specs of
the transistors in CDC's 6000 series "cordwood" modules are. Other than the
stage delay (5 ns) I have no idea.
And, as you say, an Arduino or a Pi that fits in my pocket is orders
of magnitude more powerful and costs pocket money.
The comparisons of size, power, storage, cost, power usage, heat
output and so on are often made.
What is less often observed are the facts that a machine that takes
multiple trailers can be repaired with spare parts. Anything made from
ICs basically can't, except by replacing the ICs. What if you can't make ICs any more? Or rather,
what level of IC
fabrication would it be possible to construct from scratch?
That's a fun question and a full answer would probably make a good book. For
transistors the answer is only marginally simpler. For tubes, quite a lot simpler.
(There's a nice Youtube video of someone making tubes, in his basement. You need
glass blowing equipment, a spot welder, vacuum pumps, and an inductive heating system.
That's about it for tools, as I recall. Materials: pyrex glass, kovar feed through
wires, tungsten filaments, not sure what the electrodes are made of.)
For semiconductors, you'd start with machinery to make ultra-pure materials (silicon,
I'd assume). A Czochralski crystal growing machine to make the cylinders of pure
mono-crystal silicon from which wafers are sliced. Polishing machinery. Wafer coating
machines. Wafer steppers. Etching, metal coating, diffusion, etc......... most of which
also require very pure and often exotic ingredients. (I remember being amazed to read
that chlorine trifluoride is used as a cleaner in the semiconductor industry. Look up the
properties of that compound, it will blow your mind.)
Reading the specs of the latest generation wafer steppers from ASML (the only company in
the world with the technology) boggles the mind, especially if you have some understanding
of precision machinery design. And even earlier generation steppers are not easy devices
to make. I'm not sure what's involved in doing one precise enough for, say, an
1980s era microprocessor. Or even an SN7400.
Transistors are basically the same as small ICs, unless you go to really ancient types
(point contact, mesa, alloy diffusion).
If I had to build a simple computer starting from a pile of rubble I'd seriously
consider building it from tubes.
paul