He Fixes Radios by Thinking!

Taken from “Surely You're Joking, Mr. Feynman!” Adventures of a Curious Character by Richard Phillips Feynman as told to Ralph Leighton edited by Edward Hutchings

When I was about eleven or twelve I set up a lab in my house. It consisted of an old wooden packing box that I put shelves in. I had a heater, and I’d put in fat and cook french-fried potatoes all the time. I also had a storage battery, and a lamp bank.

To build the lamp bank I went down to the five-and-ten and got some sockets you can screw down to a wooden base, and connected them with pieces of bell wire. By making different combinations of switches—in series or parallel—I knew I could get different voltages. But what I hadn’t realized was that a bulb’s resistance depends on its temperature, so the results of my calculations weren’t the same as the stuff that came out of the circuit. But it was all right, and when the bulbs were in series, all half-lit, they would gloooooooooow, very pretty—it was great!

I had a fuse in the system so if I shorted anything, the fuse would blow. Now I had to have a fuse that was weaker than the fuse in the house, so I made my own fuses by taking tin foil and wrapping it around an old burnt-out fuse. Across my fuse I had a five-watt bulb, so when my fuse blew, the load from the trickle charger that was always charging the storage battery would light up the bulb. The bulb was on the switchboard behind a piece of brown candy paper (it looks red when a light’s behind it)—so if something went off, I’d look up to the switchboard and there would be a big red spot where the fuse went. It was fun!

I enjoyed radios. I started with a crystal set that I bought at the store, and I used to listen to it at night in bed while I was going to sleep, through a pair of earphones. When my mother and father went out until late at night, they would come into my room and take the earphones off—and worry about what was going into my head while I was asleep.

About that time I invented a burglar alarm, which was a very simple-minded thing: it was just a big battery and a bell connected with some wire. When the door to my room opened, it pushed the wire against the battery and closed the circuit, and the bell would go off.

One night my mother and father came home from a night out and very, very quietly, so as not to disturb the child, opened the door to come into my room to take my earphones off. All of a sudden this tremendous bell went off with a helluva racket—BONG BONG BONG BONG BONG!!! I jumped out of bed yelling, “It worked! It worked!”

I had a Ford coil—a spark coil from an automobile—and I had the spark terminals at the top of my switchboard. I would put a Raytheon RH tube, which had argon gas in it, across the terminals, and the spark would make a purple glow inside the vacuum—it was just great!

One day I was playing with the Ford coil, punching holes in paper with the sparks, and the paper caught on fire. Soon I couldn’t hold it any more because it was burning near my fingers, so I dropped it in a metal wastebasket which had a lot of newspapers in it. Newspapers burn fast, you know, and the flame looked pretty big inside the room. I shut the door so my mother—who was playing bridge with some friends in the living room—wouldn’t find out there was a fire in my room, took a magazine that was lying nearby, and put it over the wastebasket to smother the fire.

After the fire was out I took the magazine off, but now the room began to fill up with smoke. The wastebasket was still too hot to handle, so I got a pair of pliers, carried it across the room, and held it out the window for the smoke to blow out.

But because it was breezy outside, the wind lit the fire again, and now the magazine was out of reach. So I pulled the flaming wastebasket back in through the window to get the magazine, and I noticed there were curtains in the window—it was very dangerous!

Well, I got the magazine, put the fire out again, and this time kept the magazine with me while I shook the glowing coals out of the wastepaper basket onto the street, two or three floors below. Then I went out of my room, closed the door behind me, and said to my mother, “I’m going out to play,” and the smoke went out slowly through the windows.

I also did some things with electric motors and built an amplifier for a photo cell that I bought that could make a bell ring when I put my hand in front of the cell. I didn’t get to do as much as I wanted to, because my mother kept putting me out all the time, to play. But I was often in the house, fiddling with my lab.

I bought radios at rummage sales. I didn’t have any money, but it wasn’t very expensive—they were old, broken radios, and I’d buy them and try to fix them. Usually they were broken in some simple-minded way—some obvious wire was hanging loose, or a coil was broken or partly unwound—so I could get some of them going. On one of these radios one night I got WACO in Waco, Texas—it was tremendously exciting!

On this same tube radio up in my lab I was able to hear a station up in Schenectady called WGN. Now, all of us kids—my two cousins, my sister, and the neighborhood kids—listened on the radio downstairs to a program called the Eno Crime Club—Eno effervescent salts—it was the thing! Well, I discovered that I could hear this program up in my lab on WGN one hour before it was broadcast in New York! So I’d discover what was going to happen, and then, when we were all sitting around the radio downstairs listening to the Eno Crime Club, I’d say, “You know, we haven’t heard from so-and-so in a long time. I betcha he comes and saves the situation.”

Two seconds later, bup-bup, he comes! So they all got excited about this, and I predicted a couple of other things. Then they realized that there must be some trick to it—that I must know, somehow. So I owned up to what it was, that I could hear it upstairs the hour before.

You know what the result was, naturally. Now they couldn’t wait for the regular hour, they all had to sit upstairs in my lab with this little creaky radio for half an hour, listening to the Eno Crime Club from Schenectady.

We lived at that time in a big house; it was left by my grandfather to his children, and they didn’t have much money aside from the house. It was a very large, wooden house, and I would run wires all around the outside, and had plugs in all the rooms, so I could always listen to my radios, which were upstairs in my lab. I also had a loudspeaker—not the whole speaker, but the part without the big horn on it.

One day, when I had my earphones on, I connected them to the loudspeaker, and I discovered something: I put my finger in the speaker and I could hear it in the earphones; I scratched the speaker and I’d hear it in the earphones. So I discovered that the speaker could act like a microphone, and you didn’t even need any batteries. At school we were talking about Alexander Graham Bell, so I gave a demonstration of the speaker and the earphones. I didn’t know it at the time, but I think it was the type of telephone he originally used.

So now I had a microphone, and I could broadcast from upstairs to downstairs, and from downstairs to upstairs, using the amplifiers of my rummage-sale radios. At that time my sister Joan, who was nine years younger than I was, must have been about two or three, and there was a guy on the radio called Uncle Don that she liked to listen to. He’d sing little songs about “good children,” and so on, and he’d read cards sent in by parents telling that “Mary So-and-so is having a birthday this Saturday at 25 Flatbush Avenue.”

One day my cousin Francis and I sat Joan down and said that there was a special program she should listen to. Then we ran upstairs and we started to broadcast: “This is Uncle Don. We know a very nice little girl named Joan who lives on New Broadway; she’s got a birthday coming—not today, but such-and-such. She’s a cute girl.” We sang a little song, and then we made music: “Deedle leet deet, doodle doodle loot doot; deedle deedle leet, doodle loot doot doo” We went through the whole deal, and then we came downstairs: “How was it? Did you like the program?”

“It was good,” she said, “but why did you make the music with your mouth?”

One day I got a telephone call: “Mister, are you Richard Feynman?”

“Yes.”

“This is a hotel. We have a radio that doesn’t work, and would like it repaired. We understand you might be able to do something about it.”

“But I’m only a little boy,” I said. “I don’t know how—”

“Yes, we know that, but we’d like you to come over anyway.”

It was a hotel that my aunt was running, but I didn’t know that. I went over there with—they still tell the story—a big screwdriver in my back pocket. Well, I was small, so any screwdriver looked big in my back pocket.

I went up to the radio and tried to fix it. I didn’t know anything about it, but there was also a handyman at the hotel, and either he noticed, or I noticed, a loose knob on the rheostat—to turn up the volume—so that it wasn’t turning the shaft. He went off and filed something, and fixed it up so it worked.

The next radio I tried to fix didn’t work at all. That was easy: it wasn’t plugged in right. As the repair jobs got more and more complicated, I got better and better, and more elaborate. I bought myself a milliammeter in New York and converted it into a voltmeter that had different scales on it by using the right lengths (which I calculated) of very fine copper wire. It wasn’t very accurate, but it was good enough to tell whether things were in the right ballpark at different connections in those radio sets.

The main reason people hired me was the Depression. They didn’t have any money to fix their radios, and they’d hear about this kid who would do it for less. So I’d climb on roofs to fix antennas, and all kinds of stuff. I got a series of lessons of ever-increasing difficulty. Ultimately I got some job like converting a DC set into an AC set, and it was very hard to keep the hum from going through the system, and I didn’t build it quite right. I shouldn’t have bitten that one off, but I didn’t know.

One job was really sensational. I was working at the time for a printer, and a man who knew that printer knew I was trying to get jobs fixing radios, so he sent a fellow around to the print shop to pick me up. The guy is obviously poor—his car is a complete wreck—and we go to his house which is in a cheap part of town. On the way, I say, “What’s the trouble with the radio?”

He says, “When I turn it on it makes a noise, and after a while the noise stops and everything’s all right, but I don’t like the noise at the beginning.”

I think to myself: “What the hell! If he hasn’t got any money, you’d think he could stand a little noise for a while.”

And all the time, on the way to his house, he’s saying things like, “Do you know anything about radios? How do you know about radios—you’re just a little boy!”

He’s putting me down the whole way, and I’m thinking, “So what’s the matter with him? So it makes a little noise.”

But when we got there I went over to the radio and turned it on. Little noise? My God! No wonder the poor guy couldn’t stand it. The thing began to roar and wobble—WUH BUH BUH BUH BUH—A tremendous amount of noise. Then it quieted down and played correctly. So I started to think: “How can that happen?”

I start walking back and forth, thinking, and I realize that one way it can happen is that the tubes are heating up in the wrong order—that is, the amplifier’s all hot, the tubes are ready to go, and there’s nothing feeding in, or there’s some back circuit feeding in, or something wrong in the beginning part—the HF part—and therefore it’s making a lot of noise, picking up something. And when the RF circuit’s finally going, and the grid voltages are adjusted, everything’s all right.

So the guy says, “What are you doing? You come to fix the radio, but you’re only walking back and forth!”

I say, “I’m thinking!” Then I said to myself, “All right, take the tubes out, and reverse the order completely in the set.” (Many radio sets in those days used the same tubes in different places—212’s, I think they were, or 212-A’s.) So I changed the tubes around, stepped to the front of the radio, turned the thing on, and it’s as quiet as a lamb: it waits until it heats up, and then plays perfectly—no noise.

When a person has been negative to you, and then you do something like that, they’re usually a hundred percent the other way, kind of to compensate. He got me other jobs, and kept telling everybody what a tremendous genius I was, saying, “He fixes radios by thinking!” The whole idea of thinking, to fix a radio—a little boy stops and thinks, and figures out how to do it—he never thought that was possible.

Radio circuits were much easier to understand in those days because everything was out in the open. After you took the set apart (it was a big problem to find the right screws), you could see this was a resistor, that’s a condenser, here’s a this, there’s a that; they were all labeled. And if wax had been dripping from the condenser, it was too hot and you could tell that the condenser was burned out. If there was charcoal on one of the resistors you knew where the trouble was. Or, if you couldn’t tell what was the matter by looking at it, you’d test it with your voltmeter and see whether voltage was coming through. The sets were simple, the circuits were not complicated. The voltage on the grids was always about one and a half or two volts and the voltages on the plates were one hundred or two hundred, DC. So it wasn’t hard for me to fix a radio by understanding what was going on inside, noticing that something wasn’t working right, and fixing it.

Sometimes it took quite a while. I remember one particular time when it took the whole afternoon to find a burned out resistor that was not apparent. That particular time it happened to be a friend of my mother, so I had time—there was nobody on my back saying, “What are you doing?” Instead, they were saying, “Would you like a little milk, or some cake?” I finally fixed it because I had, and still have, persistence. Once I get on a puzzle, I can’t get off. If my mother’s friend had said, “Never mind, it’s too much work,” I’d have blown my top, because I want to beat this damn thing, as long as I’ve gone this far. I can’t just leave it after I’ve found out so much about it. I have to keep going to find out ultimately what is the matter with it in the end.

That’s a puzzle drive. It’s what accounts for my wanting to decipher Mayan hieroglyphics, for trying to open safes. I remember in high school, during first period a guy would come to me with a puzzle in geometry, or something which had been assigned in his advanced math class. I wouldn’t stop until I figured the damn thing out—it would take me fifteen or twenty minutes. But during the day, other guys would come to me with the same problem, and I’d do it for them in a flash. So for one guy, to do it took me twenty minutes, while there were five guys who thought I was a super-genius.

So I got a fancy reputation. During high school every puzzle that was known to man must have come to me. Every damn, crazy conundrum that people had invented, I knew. So when I got to MIT there was a dance, and one of the seniors had his girlfriend there, and she knew a lot of puzzles, and he was telling her that I was pretty good at them. So during the dance she came over to me and said, “They say you’re a smart guy, so here’s one for you: A man has eight cords of wood to chop …”

And I said, “He starts by chopping every other one in three parts,” because I had heard that one.

Then she’d go away and come back with another one, and I’d always know it.

This went on for quite a while, and finally, near the end of the dance, she came over, looking as if she was going to get me for sure this time, and she said, “A mother and daughter are traveling to Europe …”

“The daughter got the bubonic plague.”

She collapsed! That was hardly enough clues to get the answer to that one: It was the long story about how a mother and daughter stop at a hotel and stay in separate rooms, and the next day the mother goes to the daughter’s room and there’s nobody there, or somebody else is there, and she says, “Where’s my daughter?” and the hotel keeper says, “What daughter?” and the register’s got only the mother’s name, and so on, and so on, and there’s a big mystery as to what happened. The answer is, the daughter got bubonic plague, and the hotel, not wanting to have to close up, spirits the daughter away, cleans up the room, and erases all evidence of her having been there. It was a long tale, but I had heard it, so when the girl started out with, “A mother and daughter are traveling to Europe,” I knew one thing that started that way, so I took a flying guess, and got it.

We had a thing at high school called the algebra team, which consisted of five kids, and we would travel to different schools as a team and have competitions. We would sit in one row of seats and the other team would sit in another row. A teacher, who was running the contest, would take out an envelope, and on the envelope it says “forty-five seconds.” She opens it up, writes the problem on the blackboard, and says, “Go!”—so you really have more than forty-five seconds because while she’s writing you can think. Now the game was this: You have a piece of paper, and on it you can write anything, you can do anything. The only thing that counted was the answer. If the answer was “six books,” you’d have to write “6,” and put a big circle around it. If what was in the circle was right, you won; if it wasn’t, you lost.

One thing was for sure: It was practically impossible to do the problem in any conventional, straightforward way, like putting “A is the number of red books, B is the number of blue books,” grind, grind, grind, until you get “six books.” That would take you fifty seconds, because the people who set up the timings on these problems had made them all a trifle short. So you had to think, “Is there a way to see it?” Sometimes you could see it in a flash, and sometimes you’d have to invent another way to do it and then do the algebra as fast as you could. It was wonderful practice, and I got better and better, and I eventually got to be the head of the team. So I learned to do algebra very quickly, and it came in handy in college. When we had a problem in calculus, I was very quick to see where it was going and to do the algebra—fast.

Another thing I did in high school was to invent problems and theorems. I mean, if I were doing any mathematical thing at all, I would find some practical example for which it would be useful. I invented a set of right-triangle problems. But instead of giving the lengths of two of the sides to find the third, I gave the difference of the two sides. A typical example was: There’s a flagpole, and there’s a rope that comes down from the top. When you hold the rope straight down, it’s three feet longer than the pole, and when you pull the rope out tight, it’s five feet from the base of the pole. How high is the pole?

I developed some equations for solving problems like that, and as a result I noticed some connection—perhaps it was sin2 + cos2 = 1—that reminded me of trigonometry. Now, a few years earlier, perhaps when I was eleven or twelve, I had read a book on trigonometry that I had checked out from the library, but the book was by now long gone. I remembered only that trigonometry had something to do with relations between sines and cosines. So I began to work out all the relations by drawing triangles, and each one I proved by myself. I also calculated the sine, cosine, and tangent of every five degrees, starting with the sine of five degrees as given, by addition and half-angle formulas that I had worked out.

A few years later, when we studied trigonometry in school, I still had my notes and I saw that my demonstrations were often different from those in the book. Sometimes, for a thing where I didn’t notice a simple way to do it, I went all over the place till I got it. Other times, my way was most clever—the standard demonstration in the book was much more complicated! So sometimes I had ‘em heat, and sometimes it was the other way around.

While I was doing all this trigonometry, I didn’t like the symbols for sine, cosine, tangent, and so on. To me, “sin f” looked like s times i times n times f! So I invented another symbol, like a square root sign, that was a sigma with a long arm sticking out of it, and I put the f underneath. For the tangent it was a tau with the top of the tau extended, and for the cosine I made a kind of gamma, but it looked a little bit like the square root sign.

Now the inverse sine was the same sigma, but left-to-right reflected so that it started with the horizontal line with the value underneath, and then the sigma. That was the inverse sine, NOT sink f—that was crazy! They had that in books! To me, sini meant i/sine, the reciprocal. So my symbols were better.

I didn’t like f(x)—that looked to me like f times x. I also didn’t like dy/dx—you have a tendency to cancel the d’s—so I made a different sign, something like an & sign. For logarithms it was a big L extended to the right, with the thing you take the log of inside, and so on.

I thought my symbols were just as good, if not better, than the regular symbols—it doesn’t make any difference what symbols you use—but I discovered later that it does make a difference. Once when I was explaining something to another kid in high school, without thinking I started to make these symbols, and he said, “What the hell are those?” I realized then that if I’m going to talk to anybody else, I’ll have to use the standard symbols, so I eventually gave up my own symbols.

I had also invented a set of symbols for the typewriter, like FORTRAN has to do, so I could type equations. I also fixed typewriters, with paper clips and rubber bands (the rubber bands didn’t break down like they do here in Los Angeles), but I wasn’t a professional repairman; I’d just fix them so they would work. But the whole problem of discovering what was the matter, and figuring out what you have to do to fix it—that was interesting to me, like a puzzle.