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What's Your EQ?
July 1963 Radio-Electronics

November 1961 Radio-Electronics

November 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.

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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 68.

Tricky Resistors

In the circuit shown, R1 = R2 = R3 = R4. E1, E2 and E3 are input voltages to the circuit, and are measured with respect to ground. What is the output voltage, Eo? -Earl H. Rogers

Ventilation Problem

A ventilating blower is used to vent two adjacent rooms. Each room has one light controlled by a wall switch. To comply with local building-code rules, the electric circuit must be wired so that the blower will operate only when one or both lights are on. When both lights are off, the fan will not operate. Draw a circuit using the minimum number of switch contacts that will fulfill the code requirements. -Kendall Collins

Pot Position

The ganged potentiometer is adjusted until the very sensitive ammeter reads zero. The battery and ammeter are then disconnected from the circuit, and the resistance measured between points A and C. What does the ohmmeter read? -Jack L. Shagena, Jr.

 

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

These are the answers! Puzzles are on page 38.

Tricky Resistors

Using the superposition theorem, with E2 and E3 shorted to ground, the circuit that E1 sees is:

IMAGE HERE

Note that R2, R3, and R4 in parallel equals 1/3 R. Therefore Eo = 1/4 the input voltage. Eo, as a result of E1, is -4 volts. When E2 is considered as the input, output 2, as a result of E2, is +4 volts. When E3 is considered as the input, output 3, as a result of E3, is -4 volts. Adding outputs 1, 2 and 3 algebraically, the actual total Eo with all three inputs is -4 volts.

Ventilation Problem

Two double-pole single-throw switches, connected as shown, do the job.

Pot Position

Since no current flows through the ammeter, the voltages at A and B must be equal. We can calculate the voltage at B: 2.5 volts. If the voltage at A is also to be 2.5 (which is 1/4 of the total 10 volts), both sections of the ganged pot must divide it in half. The voltage at the 10-ohm pot's wiper must be 5, and at the 12-megohm pot's wiper, 2.5. This means the pots must be exactly at mid-position.

Neglecting the very small effect of the 100-ohm section, we can see the resistance between points A and C consists of two 6-megohm resistors in parallel, so the resistance is 3 megohms.

(This is a problem that can most easily be solved "by running," or rather, by sliding.)

 
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Copyright: 1996 - 2025
Webmaster: Kirt Blattenberger,
   BSEE - KB3UON - AMA92498

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a lady's voice announced "You've Got Mail" when a new message arrived...

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