Astable Multivibrator: Round 2

Another pass at the old Squidwrench soldering project, in light of some upcoming events, seemed in order:

Astable Multivibrator - as-built - simulation
Astable Multivibrator – as-built – simulation

The 10 µF caps scale the output to visible blinkiness. Their polarity may seem backwards, but the red trace in the simulation shows that the net voltage is positive in that direction for nearly the entire cycle. They see only two forward biased junctions in the other direction, so they shouldn’t blow up.

I built it with resistors from the SqWr junk box parts cabinet that were close to the nominal values.

Connecting the transistor base / cap charging resistors to the power supply, rather than the LEDs, gets rid of the tiny current when the LEDs should be off.

The cap-and-pulse-generator dingus on the bottom kickstarts the simulation; it doesn’t have any physical significance.

Memo to Self: Build one with a pair of ET227 transistors and some 100 W tungsten bulbs…

12 thoughts on “Astable Multivibrator: Round 2

  1. Ah, the venerable Eccles-Jordan multivibrator (not to be confused with Eks). I actually built one of these out of a 12AU7 a few days ago to play with.

    1. I’ll eventually remember to take a picture of that hairball: it’s definitely not as clean as a glass tube!

  2. Memo to Self

    I’m glad I wasn’t drinking coffee when I read that…

    1. But it would work… plus, Mad Phil left me some huge bulbs that ought to be good for something.

        1. Nelson Pass: may he live forever.

          I subscribed to Audio Amateur, back in the day when I could hear music. Never built anything, of course, but I liked his designs: I could actually understand what was going on in them.

          That box o’ bulbs does have a layer of porcelain sockets in the bottom…

          1. I can still hear music, but with a Ti stapes in one ear and a plastic ceramic in the other, fidelity is a moot point. Used to have good hearing, but no more. I do recall glancing at a copy of Audiophile mag years ago and wondering just what the difference was between audiophilia (at that level) and OCD…

            Still imagining the 100W bulbs blinking back and forth for ever… I saved some tungsten (60, 75 and 100W) bulbs for our shared well pumphouse. We have good insulation in the structure, but it gets cold here… I’ve been contemplating a solar system for a new well, but one tricky part is keeping things warm without the 100W bulbs.

            1. keeping things warm without the 100W bulbs

              The original well here lived in a pit about five feet deep, so it (apparently) never got cold enough to freeze; we’re now bypassing the pump and backfeeding town water through the same pipes. I should put a datalogger in the pit to record a winter’s worth of temperatures, except for the fact that the concrete cover weighs about as much as I do. Perhaps I can suspend the logger in one of the vent pipes and call it Good Enough…

            2. The well-in-a-pit approach would eliminate the need for heat, but the real need for heat is to keep surge tanks above freezing. The current pumphouse is 6 x 8′ with a 60 gallon surge tank (R19 wall, R13 door, R30 ceiling–120 watts is enough to keep it cozy in the dead of winter), and any new one would need something similar. If I went off-grid, one of the favored approaches is to use a DC pump with multiple surge tanks. I’m thinking of a solar heating system in a really small, very well insulated pumphouse.

            3. The well tank huddled in that pit, too, although the house feed pipe had obviously been rebuilt around it; there’s some history in that copper.

              I’m definitely going to get a temperature logger down there this winter!

            4. The local geography doesn’t lend itself to big holes, unless you have a lot of determination. Shale doesn’t seem like a strong rock, until you have to dig through it. And then there’s the chunks of volcanic rock from one of the more enthusiastic eruptions a few thousand years ago. We don’t do basements around here…

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