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Here we go with three more circuit puzzlers from the November 1961 issue of Radio-Electronics magazine. The feature title, "What's Your EQ?," is a play on "IQ," but instead of Intelligence Quotient it means Electronics Quotient. The first challenge is a simple application of series and parallel resistance combinations and Ohm's Law. With the Black Box problem, don't hurt your brain too much. The author's solution is unarguably the simplest. The last, "Impossible Voltages," was devised by TV troubleshooting master Jack Darr, who publishes regular columns on the art/science, so few will probably get it right - unless you have experience with circuit containing complex mixes of resistors, capacitors, inductors, and transformers. It evidently stems from an actual case he worked on. Then again, maybe this one isn't so hard after all.

Here are a few more we hope our readers will find challenging. And if you can develop an original EQ that will stump our readers, send it to us. We pay \$10 and up for each one accepted. Write to EQ editor, Radio-Electronics, 154 West 14th St., New York 11, N.Y. Answers to October puzzles are on page 108. We just can't answer individual letters, but will continue to print the more interesting solutions (the ones the original authors never thought of!).

Current Problem

Does the meter in Fig. 1 read the same, more than or less than the meter in Fig. 2?

- Richard L. Koelker

"Black Box" Brain

Given, a "black box" having four terminals. What is the simplest network the box may contain such that the output voltage at terminals 3-4 is exactly 180° out of phase with the input voltage at terminals 1-2?

Impossible Voltages

Symptoms: Very thin white horizontal line. No vertical sweep at all.

Clues: Some very unusual voltage readings around the vertical oscillator and output stage. These include a very high negative voltage on both plate and grid of vertical output tube! This was on the order of 200 volts! Tube OK. Power supply OK.

Hint: Scope trace on plate of vertical output tube showed very high Pop voltage, at horizontal frequency. A Crosley G17TOMH.

- Jack Darr

Quizzes from vintage electronics magazines such as Popular Electronics, Electronics-World, QST, 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.

## Solutions

A Current Problem

Both meters read the same current. This is an example of the reciprocity theorem, which states:

If an emf of any character located at one point in a linear network produces a current at any other point in the network, the same emf acting at the second point will produce the same current at the first point.

Impossible Voltages

The 30-μf electrolytic capacitor, connected between the arm of the vertical linearity control and chassis, was completely open. This evidently allowed the vertical oscillator and output stage to go into some kind of wild oscillation, at or near the horizontal frequency (it was never exactly traced out) which accounted for the appearance of the high negative voltage at the plate of the output half of the 12BH7.

Black Box Brain Twister

The wires are crossed, from terminal 1 to 4 and from 2 to 3.

Posted July 18, 2024