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.
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!)
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!
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!
Update: 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.