You will probably breeze through both of these "What's Your EQ?" circuit challenges in the February 1967 issue of Radioâˆ’Electronics magazine. Don't look too deeply into what is presented. Both require figuring the voltage between two points. For the Zener Limiting Circuit, just apply basic knowledge about zener diodes. The "Voltage Problem" circuit requires a simple summing of voltages around the single loop to derive the current, then calculate the voltage across R1 to get VB. VA is a no-brainer. The depiction of the DC sources is a bit wonky; the voltages shown are the totals for the each group of cells (aka battery), not per cell.

Conducted by E. D. Clark

Zener Limiting Circuit

Three Zener diodes, each rated at 3/4 watt, are connected as shown to expand a voltmeter scale. What's the voltage between A and B?

- Kendall Collins

Voltage Problem

What's the voltage between A and B?

- John. A. Reeder, Jr.

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.

Zener Limiting Circuit

The applied voltage through the limiting resistors operates the Zeners at their rated voltages. Thus A is -10 volts with respect to ground - the sum of D1 and D3 voltages. Similarly, B is -30 volts with respect to ground - the sum of D2 and D3 voltages. Hence, a difference of 10 volts is found between A and B.

When the applied voltage is less than -20, the Zeners won't conduct, and practically zero volts will exist between A and B. Between -20 and -30 volts applied, D1 and D3 will conduct, while D2 won't. Voltage from A to B will vary between zero and 10.

Voltage Problem

Between A and B there is zero voltage.

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.

Posted April 18, 2023