Retrotechtacular: Donner 3500 portable analog computer


What if we told you we had a computer you can take with you? What if it only weighed 28 pounds? This is a pretty hard sell when today you can get a 1.5 GHz quad-core processor packing computer to carry in your pocket which weighs less than 5 ounces. But back in the day the Donner 3500 was something to raise an eyebrow at, especially for tinkerers like us.

The machine was unveiled in 1959 as an analog computer. Instead of accepting programs via a terminal, or punch cards, it worked more like a breadboard. The top of the case features a grid of connectors (they look like banana plugs to us but we’re not sure). The kit came with components which the user could plug into the top to make the machine function (or compute) in different ways.

We’re skeptical as to how portable this actually was. It used vacuum tubes which are not fans of being jostled. Still, coming during the days when most computers were taking up entire buildings we guess the marketing claim holds up. If you’d like to see a bit more about the machine’s internals check out this forum post.


  1. Ren says:

    Radio Shack used to sell a “computer” kit, that required placing jumper wires in the panel on top.

    • Ren says:

      • RoadWarrior222 says:

        Innnnteresting, most of the “programming” seems to be in the overlays, and what it can train the operator to do… But curious as to what actual smarts are in that little black clump in the wiring.

        • macegr says:

          Absolutely nothing, that’s just a wire nut. It looks like someone took it apart to make it do something else. There are no electronics whatsoever, it’s basically a bunch of light bulbs and ganged slide switches.

          • RoadWarrior222 says:

            Heh, probably why the box promises the “excitement” of your own computer, ‘coz it’s bit short on the computer.

          • DiHydrogenOxide says:

            I actually had one of these as a kid. Rather disappointing for a “computer,” but in reality it does perform logic switching as per the switches and the wiring. Sadly, the monkey is the system clock…

          • RoadWarrior222 says:

            ^^^ LOL the old monkey in the loop technology.

  2. Peter says:

    DONNER: because there’s no party like a Donner party!

  3. ka1axy says:

    Analog computers always fascinated me. I’v never used one, nor met anyone who has. But the idea of building an analog (in the sense of “simulation”) of an equation, then being able to vary the input quantities and immediately see the change in the output — well, it’s kind of like a “linear spreadsheet”, isn’t it?

  4. Alex says:

    If you want to see more analog computer stuff, here’s a video of an analog bouncing ball simulation. It may even have been posted on hackaday, but I’m not sure. Either way…

  5. Frank Incensed says:

    “We’re skeptical as to how portable this actually was. It used vacuum tubes which are not fans of being jostled.”

    VTs don’t like to be dropped/smashed, that is true. But I think that their fragility is often overstated. Believe it or not, vacuum tubes were used in proximity fuses in artillery shells in WW2. Consider the G-forces a tube would experience being hurled out of the barrel of a cannon.

    More commonly, tubes have successfully taken a beating in “portable” devices like radios and amplifiers for many decades. Those heavy steel corner guards on your guitar amp head are not there because the manufacturer thinks the device will be babied.

  6. I don’t know about that claim that tubes hate being jostled. I can name at least a dozen cars from the 1950s and before which had tube radios that worked reliably for years. In fact, the most common failed part in the old tube car radios was called a “mechanical vibrator.” Plenty of tubes can withstand typical transport bumps.

    • Bill says:

      The photos of the inside of the computer even show springs to keep the tubes seated in their sockets.
      I suspect the tubes in Soviet fighter jets got jostled a bit.

    • Derive this! says:

      Yeah. Vibrators were how you got HV for the tubes, rather crude but effective. A lot of old novelty shocking devices like shocking lighters worked much the same way.

      • RoadWarrior222 says:

        I was trying to figure how to make a vibrator out of a mechanical buzzer…. but buggered if I can find anywhere to get a mechanical buzzer any more either. (it was gonna be a low buck workaround to something, so probably no point pointing me to $$$ vintage parts)

        • Ren says:

          Think “electric school bell” it is a relay/solenoid that when energized, pulls the plunger into the coil. The plunger opens a switch in series with the coil, shutting it off. A spring then pulls the plunger out and closes the switch and then re-activates the coil. Cycle repeats, and repeats…. The is also attached to the clapper for the bell. The frequency of the cycle is largely determined by the physical characteristics of the mechanism, as well as the inductance of the coil and the voltage it receives. A multi-vibrator is similar
          but it uses the on/off switching of the voltage in the input of a transformer or auto-transformer to produce a higher voltage in the secondary (the same principle is used to generate the thousands of volts for a spark plug from the 12 volt battery in a car.

  7. selim13 says:

    Awesome device!
    Here is a link to small article about Soviet analog computer: (russian).
    It is not tube based – more modern.

  8. Mike Turner says:

    A long time ago, I programmed analog computers or school. They were no more difficult to use than a modern computer for modeling equations. Both magnitude and time scaling were sometimes needed but modern digital computers can also bite you for the same things.

  9. localroger says:

    There was plenty of portable tube equipment, although lots of it would better be described as “luggable.” I have a tube-based VTVM that isn’t much larger than a high end modern multimeter. There were special sockets and clamps for securing tubes in vibration and shock situations. The giveaway that this device was meant to be carried around is the leather handles.

  10. Derive this! says:

    Ha, tubes in soviet jets… There are still tubes in just about every fighter, warplane or rotary wing craft out there actually. Maybe not for computational needs exactly, but…
    And there are tube types that were built to be a little more rugged with better internal support structures and such along with a clip or can or external dampening. But yeah, filaments become brittle after being used, so don’t want to give them any rough loven’ or hard shocks for sure.

  11. Frantone says:

    I have owned several analog computer components of the years – all now passed along to others. You are correct about the banana plugs… that is indeed what they used for the patch bays. During WWII vacuum tubes were developed for tanks and aircraft that were literally indestructible by shock or vibration, and after the war the engineering world was fueled by war surplus components. I have many JAN tubes, and even some of those glass cased tubes are rated for over 20g’s.

  12. echodelta says:

    Wow it has one, ten turn pot! One knob that could be set to one part per one thousand.

  13. cplamb says:

    Hardly the smallest analog computer available. Slide rules could be much smaller.

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