[vcf-midatlantic] vacuum tube computers, was Re: Museum Report 2017-11-26 November 26, 2017

Dave McGuire mcguire at neurotica.com
Mon Nov 27 13:47:52 EST 2017

On 11/26/2017 09:13 PM, Jeffrey Brace via vcf-midatlantic wrote:
> How would you explain the George Philbrick machine to an 8 year old?

  Well, as you know it's critically important to tune your presentation
to the level of the guest.  When starting a more personal tour of LSSM,
we usually find a non-intrusive way, starting out with reading body
language etc, to ask a person what their levels of technical knowledge
and interest are.  Then we explain things in different ways, on
different levels, based on that.

  For a total technical neophyte, our explanations are more geared
toward talking about how what we have now (holding up my smartphone)
wouldn't exist without having first passed through all of these
(gesturing toward the exhibit floor) phases of development, then go to
some specific stories as to how and why.

  For an EE or CS person with a background in electronics and/or
processor architecture, that's a waste of time.  We go into things like
"this machine is a 12-bit system implemented using all 7400-series TTL
chips" when I fire up the PDP-8/e.  I talk about "no chips at all, all
discrete transistor logic" when we walk past the table of Straight-8s.

  While the LSSM doesn't have anything like the Philbrick system, we do
have a Heath H-1, another late-1950s tube-based analog computer.  To a
young person, we'd explain that it was used by scientists and engineers
to perform calculations for designing planes and big buildings.  It's
complicated, look at all those knobs!

  But to an EE/CS person who maybe doesn't know about analog computers
(most haven't), we explain that it's a system with no bits, just
voltages representing physical quantities, and most importantly it's not
a discrete system, but a continuous system.  These operational
amplifiers (gesturing toward the op-amps) and resistors can be wired up
to perform most any mathematical primitive, and wired together with
capacitors to perform integration and differentiation, to solve the
differential equations that most every real-world process is based on.

> How do you explain what a vacuum tube actually does to an 8 year old?

  I wouldn't, as there's essentially no chance that he/she would be
interested or have the background to be able to understand it.  See
above. ;)


Dave McGuire, AK4HZ
New Kensington, PA

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