Books from my collection.

Found in Books: Evil Plans?

Welcome to the second installment of Found in Books! Today we have an intriguing scrap of paper I found in an old schoolbook.

Electrical sketch and old physics school book.

The book is a secondary level physics book from about 1945. It’s hard to say when the drawings on the scrap were made, but the paper is strongly discoloured by age (it looks like it used to be your standard white ruled paper) so it’s probably been in the book for a while. (If anyone knows how to better date things like this, let me know!)

Electrical circuitry drawn on a scrap of paper.

On this side of the scrap we seem to have a design for an elaborate electrical circuit with a whole lot of resistors, capacitors, transformers, and a few things I don’t recognize. The two oval shapes are a mystery to me, and I have no idea what this circuit is supposed to do. Maybe it doesn’t do anything. (I can’t seem to discover a power source in the circuit.) It could just be a doodle by a bored student; on the other hand, the components of the circuit are meticulously labeled and the figure as a whole also seems to have a label, ‘EF9.’ Strange!

Back side of electrical sketch with more drawings.

And here we have the backside of the same scrap of paper. On the right half, just some doodling, and on the left two more, nearly identical designs labeled ‘EBL1’ (or EBLI?) and ‘EF6.’ Again, I’m clueless as to what these are supposed to represent. The top parts are ovals like in the previous picture, and the bottom parts are, what, time bombs? That’s the only thing they remind me of.

The bottom line is, this little scrap of paper is a mystery to me. Did a student draw these? Was this part of a school exercise? Was he designing his evil lair and plotting world domination? Or was he just doodling randomly? Where is the rest of the paper and might that have contained more clues as to what these drawings are?

Or were these drawings perhaps made by a teacher? (I don’t know whom the book belonged to.) Of course it is possible that the drawings have nothing to do with the schoolbook at all, but ended up in it for some other reason. Who can say?

If you have any light to shed on what we’re looking at here, do let me know!

EBL1 vacuum tube schematicUpdate: Several suggestions are in about the drawings and we’ve made some progress. The oval objects are definitely vacuum tubes and the labels indicate the type of tube. So far suggestions for the big circuit as a whole are an amplifier or a radio transmitter; but we’re not yet sure. The ‘time bombs’ may be, as John commented below, multi-pole switches, although that doesn’t help me understand what the diagram is supposed to be. However, we may solve these mysteries yet!

Update 2: The Internet rolled up in its Mystery Machine and solved the heck out of this. The schematic definitely seems to be a vacuum tube amplifier, as per general consensus on Reddit and in the comments below. It also definitely looks quite a bit like this (cleaner) schematic. The back of the scrap just shows drawings of the vacuum tubes used with the layout of the connections. The lines indicate which connector connects to which part of the vacuum tube. Compare for example with the image from the datasheet of the EBL1 vacuum tube on the right.

Marco is a theoretical (bio)physicist, currently engaged in unraveling the sequence-dependent dynamics of DNA molecules to earn his PhD at Leiden University. Other passions include literature and history.

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  1. John

    Hi Marco, I think those ovals are transistors and the ‘time bombs’ are multi-pole switches, but it’s been a while since I’ve done any electronics. I think you should build it and see what it does!

    • Hey John,

      Someone else suggested vacuum tubes for the ovals; the labels starting with an E seem to correspond to types of vacuum tubes. So basically, the precursors to transistors.

      Would multi-pole switches just be switches that can connect one contact to one of N other ones? I wonder what the point would be of hooking one up to just the different ends of a vacuum tube…

  2. Oldschool

    They are vacuum tubes. They are multiple pins in a vacuum tube. Transistor’s simplification of wiring is one of the (vast list) of reasons they superseded tubes. No need for HV in a solid state circuit.

    • Yeah, this seems to be what the ‘time bombs’ are, just the undersides of the vacuum tubes. Thanks!

  3. akfrnswrth

    I am positive that this is an audio amplifier. The ovals represent tubes, and the “time bombs” look like a sketch of how the bases of the tubes are wired. The power source is not well-marked, but the transformer on the far right connects to mains across the two dots. The little triangle drawn on the right side of the smaller transformer is a speaker. The audio input is on the far left.

    • This definitely seems to be the most likely answer. But is it a sort of two-step amplifier, since it has two vacuum tubes? And what are all the many capacitors etc. for?

    • Zack krasowski

      Yes the “time bombs” are wiring pinouts for the octal tube sockets (the bit the tube actually plugs in to). Looks like a simple audio amp.

  4. RadioHacktive

    This seems to be a schematic for a 1930s phonograph audio amplifier. The vacuum tube type is consistent with that era. The style and detail makes me think the drawer was copying an example circuit from a vacuum tube data manual, probably Philips.
    During the great depression, paper was hard to get, so scraps were reused.

      • Interesting link. You think the scrap itself is from the 30s? That would make it a lot older than I had guessed. (Which would be cool, though.) What makes you think it is specifically a phonograph amplifier? Someone else remarked that the part at the top, with the sliding resistor, might be for tone control. Would that be consistent?

        By the way, is there a particular reason you think it was copied from a Philips manual, other than the fact that I found this in a Dutch book?

        • RadioHacktive

          Re:30s – The tube designs seem to be at that awkward, still developing style the early 30s had. Like the control grid connecting to a separate pin on the glass envelope instead of a pin in the base that later tube designs used. One of the big problems tube designers had back then was stopping spurious oscillations at radio frequencies just in the tube itself. It wasn’t until WW2 days the internal designs improved that standard octal sockets could be used.

          Re:Phono Amp – The input impedance is just right for the early piezoelectric pickups. I haven’t tried to analyze the tone circuits, that might yield another clue. It seems at first glance to be a low-pass filter function since it’s in a negative feed back loop from the plate electrode to the the control grid. But the switch with capacitors makes me wonder why both those and the adjustable control.

          Re:Philips manual – I thought it likely due to location, but it could have been other company’s manuals. I don’t know who made the EBL1, EF6 tubes.

  5. f m

    This is a lamp transceiver circuit that needs to be corrected

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