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What's Your EQ?
October 1962 Radio-Electronics

October 1962 Radio-Electronics

October 1962 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.

sink-me

What's Your EQ?

Three puzzlers for the student, theoretician and practical man. They may look simple, but double-check your answers before you say you've solved them. If you've got an interesting or unusual answer send it to us. We are especially interested in service stinkers or engineering stumpers on actual electronic equipment. We are getting so many letters we can't answer individual ones, but we'll print the more interesting solutions (the ones the original authors never thought of). We will pay $10 and up for each one accepted. Write EQ Editor, Radio-Electronics, 154 West 14th St., New York, N. Y.

Answers for this month's puzzlers are on page 91.

What's the Impedance?

In this parallel circuit, at what frequency is the impedance at a maximum? (Note well that the capacitance is 2 farads, not microfarads.) -Harold F. Tolles

A Pad Puzzle

Five resistors are connected in a typical H-pad circuit. An ohmmeter connected between A and B shows a resistance of 308 ohms. A second measurement is taken with two jumpers in the circuit. One jumper is connected from A to C and the other jumper from B to D. The ohmmeter now shows 188 ohms. Find the values of R1 and R2, if the four resistors marked R1 are equal. -Kendall Collins

More TV Trouble

The picture locked in horizontally but it was critical. Tearing and jitter as well as intermittent bending made the picture unwatchable. Suspecting electrolytic C, we checked the waveform across it with a scope. Instead of being clean as it should have been, various random pulses, continually changing, indicated that the electrolytic was open. Certain that we had found the trouble, we installed a new electrolytic. When we turned the set back on, there was no high voltage and no drive voltage from the horizontal oscillator on the horizontal output grid. Disconnecting the new electrolytic, the raster came back on but still with the old trouble. The new electrolytic was good. What was 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

Answers to Puzzles on p. 54

What's Your EQ? Solutions

What's the Impedance

This is known as "The Singular Case of Parallel Resonance" with the relationship R1 = R2 = √L/C. If calculated as two parallel impedances, it will be found that Zin is 2 ohms at whatever frequency it may be measured.

A Pad Puzzle

The first ohmmeter reading shows R1 + R2 + R1, a series combination that equals 308 ohms. (R1 and R2 are 120 and 68 ohms. respectively.) This is changed to 2R1 + R2 = 308. The second ohmmeter reading shows 1/2 R1 + R2 + 1/2 R1. This changed to R1 + R2 = 188. Subtracting, we have

2R1 + R2 = 308

R1 + R2 = 188

R1 = 120

and R2 = 188 - 120 = 68

More TV Trouble

Cathode resistor R2 had changed to less than 100 ohms. This, for all practical purposes, eliminated the normal feedback voltage required to sustain oscillation. The open electrolytic, though, provided an alternate feedback path, since the 10,000-ohm resistor R1 was now common to both triodes. When a new electrolytic was installed, there was no feedback, and the oscillator (and high voltage) ceased operating.

Installing a new electrolytic and a 1,000-ohm cathode resistor solved the whole problem.

 

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