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What's Your EQ?
July 1961 Radio-Electronics

July 1961 Radio-Electronics

July 1961 Radio-Electronics Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Electronics, published 1930-1988. All copyrights hereby acknowledged.

Here we go with three new "What's Your EQ?" challenges from the July 1961 issue of Radio-Electronics magazine. Readers submit the problems, which typically involve creating a circuit to perform a specified function, or determining how a given circuit works. The first of these is more of a puzzle, since the author shows you how to go about arriving at the answer. Since incandescent light bulbs are not overly familiar to a lot of people these days, it might be to the advantage of pre-Millennials who grew up using them and are acquainted with their properties. The second is an old-fashioned Black Box challenge that some readers will solve without much trouble. The last is a service TV troubleshooting problem that almost nobody will get, although I know a least three RF Cafe visitors who can probably figure it out.

What's Your EQ?

Answers to last month's puzzles, with comments on the May quiz, are on page 72.

We can still use brain-teasers on the engineering level - are swamped with simple ones and TV problems. $10 will be paid for each one accepted. Address Puzzle Editor, Radio-Electronics, 154 W. 14 St. New York 11, N.Y.

Parallel Bulb Puzzler

Parallel Bulb Puzzler - RF CafeThis is a game. It is intended, not only to mystify those of your friends familiar with straightforward parallel circuitry, but to confound them to a point of sheer frustration. They have before them five ordinary light bulbs of varying wattages connected in parallel. Merely by turning each bulb into its socket, one at a time, they are to light all four bulbs but the middle one - the 75-watter. According to all laws this should be easy; but they find that by turning in the first bulb nothing happens. Turn in the second bulb, all others turned out, and it glows. Now turn in the first bulb again, and the second one goes out. Or, turn in bulbs two and five, and both glow. Now turn in any remaining bulb and they will all go out. This mystification will prevail until the bewildered one discovers that bulb three responds rather peculiarly in respect to the others. Presto - with a little logic he has it and all the bulbs but the middle one are glowing with about the same intensity. What adds to the confusion is that the first bulb, a 40-watter, will not glow when turned in, and this discourages the puzzler from trying the larger 75-watter which, after all, is not to be lit. But turn it in, and there it is glowing. This, only if all the others are turned out.

The circuitry is very simple (see figure) and need not be concealed from your victim. It is better, in fact, to build it in a plastic box, and wire the sockets so he can see the parallel connections.

Two questions:

1. Why does the circuit act as it does?

2. What are the values of C and L? (We can tell you that is a filter choke and that C should be non electrolytic. )

C - ?

L - ?

R1, 2, 3, 4, 5 - Ordinary 120-volt electric light bulbs. Suggested values: R1 -40 watts; R2-15 watts; R3-75 watts; R4-25 watts; R5-15 watts.

- Martin. H. Patrick

 

Resistor Black-Box Puzzler - RF CafeResistor Black-Box Puzzler

The ingenious little brain twister below is reprinted from the April 1961, issue of Electron Bulletin, Cleveland Institute of Electronics:

Three leads, marked A, Band C, feed into a box containing three resistors. Measuring with an ohmmeter, the resistance between A and B is 30 ohms, between Band C 40 ohms, and between A and C 50 ohms. Draw a diagram showing how the resistors are connected, and the resistance of each of them.

There are at least two solutions for this problem. You will find the easy one fairly soon. Now find another hookup that will give you the same ohmages between terminals.

 

What's the Trouble?

What's the TV Trouble? - RF CafeThis Westinghouse V2411 chassis was lugged into the shop by the outside technician for the condition shown in the picture: a bright horizontal bar about an inch wide across the upper center of the raster. The technician had changed the 6EM7 vertical oscillator output tube in the home but it had no effect. Moving the height and linearity controls widened or narrowed the bar but did not remove it. The shop technician made a couple of exploratory checks and announced that the trouble was a fairly simple, though unusual, one that could have been repaired by the technician in the home. What's the trouble?

- Wayne Lemons


Quizzes from vintage electronics magazines such as Popular Electronics, Electronics-World, QST, Radio-Electronics, and Radio News were published over the years - some really simple and others not so simple. Robert P. Balin created most of the quizzes for Popular Electronics. This is a listing of all I have posted thus far.

RF Cafe Quizzes

Vintage Electronics Magazine Quizzes

Vintage Electronics Magazine Quizzes

Vintage Electronics Magazine Quizzes

Solutions

Parallel-Bulb Puzzler

Parallel-Bulb Puzzler Solution - RF CafeThe theory of operation is based on the fact that a series-resonant circuit will pass a maximum current when it is in resonance with the frequency of the supply source. In this case it is 60 cycles. Included in the circuit is also a resistor in the form of a 75-watt bulb. By changing anyone of the three values - inductance, capacitance, resistance - we upset the balance of the resonant circuit, and thereby decrease the current.

To make this puzzler, select a filter choke of about 0.5-henry inductance and about 60 ohms dc resistance. Set up the experiment as shown in the figure, using any available filter choke handy. Start with a 1-μf nonelectrolytic capacitor. Turn the 40-watt bulb into the socket. If it lights, turn it out again and add another 1-μf capacitor in parallel with the first. Continue this in small steps, adding preferably 0.5-μf capacitors until the 40-watt bulb fails to light. Now turn in the 75-watt bulb, and it should glow. All that remains is to connect three similar sockets and insert in them bulbs of smaller wattages, such as a 25, 15 and another 15.

A word of caution when working on your experimental hookup: You are leading line voltage out onto your bench - be careful! Also the capacitors store up a considerable charge - don't think the circuit is "dead" when you pull the plug. Screw in a lamp and discharge the capacitor. And, be sure you have only one bulb turned into its socket when you are experimenting for the proper value of capacitance.

When you get the proper value, a single capacitor (or two if necessary to get the correct value) may be substituted and the unit built into a box for demonstration purposes. It is a good idea, as stated before, to make the top panel plastic and keep the wiring in plain sight so the parallel connections can be seen plainly. This adds greatly to the mystification.

Observe that, by taking resistance out of the resonated circuit (turning the bulbs in decreases the resistance in the parallel bulb circuit), we do not unbalance the resonant period greatly. On the other hand, by increasing resistance (turning the bulbs out), we reach a definite point where the circuit suddenly drops out of resonance.

Resistor Black-Box Puzzler Solution - RF CafeResistor Black-Box Puzzler

Resistance between A and B is 30 ohms; between B and C 40, and between A and C, 50 ohms. The easy answer is at the left. But, where resistors can be hooked up in Y-formation, they can also be hooked up in delta with the same results, as shown at the right.

What's the Trouble

Since the set was nearly new, the shop technician decided to make a couple of localizing checks before pulling the chassis (always a good idea). He replaced the 6EM7 vertical oscillator output again, but, as the outside technician had noted, it did not cure the fault. Looking at the circuit, he saw that the sync separator might be introducing the bar, or that perhaps the video amplifier was in some way superimposing the bright bar. The shop technician localized the trouble to these stages by pulling one tube, the 6EB8, which was both the video amplifier and the sync separator. With the 6EB8 out, the bright bar disappeared. A new 6EB8 cured the trouble. The original tube was checked and found to have a slight leakage from heater to grid and heater to cathode of the triode section.

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