[vcf-midatlantic] vacuum tube computers

Dean Notarnicola dnotarnicola at gmail.com
Mon Dec 4 13:32:29 EST 2017

This may be one of the clearest explanations of analog commuting I've
heard; and I'm going to steal it while docenting :-)

Thanks, Herb!

On Mon, Dec 4, 2017 at 12:18 PM Herb Johnson via vcf-midatlantic <
vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:

> The discussion below concluded in late November, but I have some
> comments and considerations.
> First, I'll say that there's any number of explanations available, for
> the history of computing technology and use. The person or institution
> doing the explaining, has their own objectives. The item has its time
> and place, and has levels of technology in it. And, there's sometimes
> consideration of the audience (child, expert in X but not Y, etc.).
> So - no right and singular answers to questions of presentation. I'll
> give or support a view for my own reasons.
>   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
> I have to agree with earlier posts by David Gesswein, who stressed the
> point that analog computers solve "differential equations". And all have
> mentioned in various ways, that analog computers use voltage-levels, not
> "bits", to represent the values computed. Those are fundamental
> considerations from my view. Other people have other views, I won't
> argue much with them - I'm arguing with people who are still choosing
> what views to consider.
> My view is, as a BSEE educated in the 1970's about both analog and
> digital circuits, who saw analog computers in use in academia and in the
> factory, who worked on one or two of them in my working lifetime. The
> hardest thing about explaining analog computing, is that it's almost
> TOTALLY EXTINCT today. It's hard to think or talk about something,
> outside your experiences. And preservation of extinct computing - and
> explaining it in it's own context - matters to me.
> One can explain "voltages not bits", in any number of ways, appropriate
> to audiences and settings. "Temperature" might be a good example.
> There's still mercury thermometers, mechanical thermostats and
> mechanical thermometers. They use the expansion of metals in an ANALOG
> way, to represent "temperature". The Weather Channel, gives it some
> number. But we feel "hot" or "cold" without numbers in our heads. A
> point to consider: the physical world is not lists of numbers, it's
> events and materials and the flow of time.
> "Differential equations" is jargon used by engineers and scientists. But
> it comes down to actions in systems over time. How fast does water boil
> on the stove? Or freeze if put outside in the winter? How long does it
> take your car to go from zero to 60? How long does it take a
> baseball/football in flight to be caught? These are ANALOG values that
> change with time. And, there are analog circuits (components wired up)
> which can represent these rates-of-change calculations. Then you feed
> those circuits the analog values as voltages, and watch what they do
> over TIME. *That* is what an analog computer is about. Circuits and
> components, wired for one computation, using time and voltages to
> represent values - no "bits", no digital (except for numeric results or
> inputs).
> I myself, don't tell people "this is too complicated to explain". I give
> them *something*; it will provide some impression and place to start;
> further consideration will be their choice to make.
> So. I hope the two explanations above, of "voltages not bits" and
> "differential equations", are helpful. I hope the notion of "extinct
> computer preservation" gets some attention. Otherwise, I'm not going to
> debate some ultimate description or how-to-talk-to methods. I've
> explained why, and I've offered my own views.
> Herb Johnson
> retrotechnology.com
> PS: a vacuum tube, controls electrons going from a hot metal to a metal
> plate. The flow of electrons is a current, like water from a faucet. The
> current is controlled by the electrons going through a grid. a grid is
> wires strung across the current-flow, which repel the electrons like
> magnets do. Just as you can control water by turning a faucet, you can
> control electric currents with a vacuum tube, by changing voltages on
> its grid. Old radios and TV's, very old computers, used vacuum tubes.
> --
> Herbert R. Johnson, New Jersey in the USA
> http://www.retrotechnology.com OR .net

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