Please Support RF Cafe by purchasing my  ridiculously low−priced products, all of which I created.

The January 1967 instance of Radio−Electronics magazine's "What's Your EQ?" challenge contains only two puzzles. The first is a variation on the classic resistor mesh wherein a matrix of series and parallel resistors, all of a common value (10 Ω), are wired together, and your job is to determine what total resistance would be measured between the indicated two points. Author E.D. Clark implicitly suggests taking a good look at the schematic to simplify it before diving into it with circuit analysis equations. Maybe cross your eyes a bit and cross-focus like you do with those 3D images that were popular a couple decades ago. You'll be amazed (see what I just did there?) at how simple it is to calculate the equivalent resistance. The second puzzle takes a bit more work. No restrictions are placed on what additional components can be inside the boxes. To clarify, if the top switch and bulb are labeled "A" and the bottom one "B," then switch "A" switch independently controls (on or off) only bulb "A" and switch "B" switch independently controls (on or off) only bulb "B." The third wire mentioned for a simple connection would be a common point for the current flow.

Conducted by E. D. Clark

Two puzzlers for the student, theoretician and practical man. Simple? Double-check your answers before you say you've solved them. If you have an interesting or unusual puzzle (with an answer) send it to us. We will pay \$10 for each one accepted. We're especially interested in service stinkers or engineering stumpers on actual electronic equipment. We get so many letters we can't answer individual ones, but we'll print the more interesting solutions - ones the original authors never thought of.

Write EQ Editor, Radio-Electronics, 154 West 14th Street, New York, N. Y. 10011.

Answers to this month's puzzles are on page 99.

Resistor Network

Another insomniac's RT nightmare.

Forget about Kirchhoff's laws and loop-circuit calculations, though. Study the diagram carefully for about 30 seconds.

What's the total resistance at the terminals?

- Dennis Howard

Light Switching Circuit

Either one or both of the lamps in box B may be turned on by throwing either one or both of the switches in box A. In normal electrical work, this hookup would require three conductors between the boxes, not two, as shown.

What's inside the boxes and how is everything wired?

- Jim Wilhelm

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.

These are the answers. Puzzles are on page 61.

Resistor Network

The total resistance is 2/5 ohm. Yes, all resistors are in parallel!

Light Switching Circuit

The reverse resistance of the diodes (any receiving-type silicons) blocks current flow to both lamps when both switches are open. When S1 is closed, current flows through D3, L1, D2, lighting L1. But current cannot flow through L2 because D2 and D4 are back to back in series with L2, blocking current flow on both half-cycles of the ac.

Posted November 29, 2023