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What's Your EQ?
April 1964 Radio-Electronics

April 1964 Radio-Electronics

April 1964 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.

Finish up your week by considering these three "What's Your EQ" circuit challenges that appeared in a 1964 issue of Radio-Electronics magazine. They were submitted for consideration by readers, and sometimes by staff writers. The first is yet another form of the Black Box mystery component. Kendall Collins sort of gives away part of the answer in the problem statement. The second is a fairly straight-forward switching circuit. You'll get it with no problem. The third is most challenging. Don't be put off by the presence of a vacuum tube in the schematic. Mentally replace it with a FET and go from there. Interestingly, there is a lot of forum chatter about the Dynakit "Stereocator" feature regarding stereo reception. Those of you familiar with tuning receivers that used point-to-point wiring in a chassis that did not provide much in the way of shielding will probably quickly get the answer.

What's Your EQ?

What's Your EQ?, April 1964 Radio-Electronics - RF CafeWe're always interested in valid solutions the puzzles' authors didn't think of, and we'll print the most interesting. We pay $10 apiece for really good stumpers, especially genuine design and service problems. Write EQ Editor, Radio-Electronics, 154 W. 14th St., N. Y. 10011.

Answers to these puzzles are on page 77.

Take Two Meters - RF CafeTake Two Meters

In this circuit, a 115-volt ac source is connected across terminals A and B. The load consists of an ac ammeter in series with a 100-ohm resistor which is connected to a dc ammeter shunted by a black box. Both ammeters have identical d'Arsonval mechanisms.

The black box contains a solid-state device that functions as a closed switch during one alternation of each cycle, and an open switch during the next alternation. What is "the reading of each ammeter? What is in the black box?

- Kendall Collins

 

Design Problem

Given the following components:

1 spdt switch (A)

1 spst switch (B)

1 dpst relay (appropriate coil rating)

1 lamp (appropriate voltage and wattage)

Design a circuit so that:

1. When switch A is off, switch B controls the lamp.

2. When switch A is turned on, the lamp remains in the state it was before switch A was turned on. Switch B has now lost control and can be flipped back and forth with no effect. When A is turned off, the lamp immediately assumes the state of switch B. Switches are not operated simultaneously.

- William M. Waite

 

Full-Time Stereo - RFCafeFull-Time Stereo

A kit-builder friend of mine was quite frustrated after constructing and aligning a Dyna stereo tuner with built-in multiplex integrator. The electron-ray Stereocator indicated that all broadcasts were stereo! The figure shows the frequency-doubler circuit Dyna uses. With T2 tuned to 38 kc (the "second harmonic distortion" of the 19-kc input), a 38-kc output is obtained whenever a stereo program with its 19-kc pilot signal is tuned in. The 38-kc signal is used in the detection process (it's automatically in phase with the pilot, as required) and is also fed to the eye tube to indicate the presence of a stereo signal,

The only trouble with the set in question, however, as a scope readily verified, was that a 38-kc output was present even when there was no 19-kc input at all! Somehow the frequency doubler had become an oscillator.

The capacitors all checked out OK and the wiring layout matched the pictorial. The alignment instructions had said to adjust T1 and T2 for the maximum 38-kc output (using the eye tube as an indicator) when the pilot is present. I verified with my scope that the 38-kc output did indeed drop as either T1 or T2 was detuned from the positions my friend had found. Knowing Dyna's usual high quality, it was hard to believe that there could have been anything marginal about the original design. For a while I was stumped, but then I figured out the simple explanation. Can you?

- Joel H. Levitt

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 What's Your EQ?

This month's puzzles are on page 42

Take Two Meters Solution - RF CafeTake Two Meters

The ac ammeter is calibrated in rms values and reads 1.15 amperes. This can be computed by Ohm's law. The rms voltage drop across the resistor, divided by the resistance, equals the current, which is the same through all elements of this series circuit.

115 volts / 100 ohms = 1.15 amps

The black box contains a solid-state diode which short-circuits the dc ammeter terminals during each negative alternation. As a result, half-wave current flows through the dc ammeter. The scale is calibrated to show average current values and the pointer takes a position representing 0.515 ampere. This reading is 0.318 of the peak value of the half-wave current flowing through the dc ammeter.

 

Design Problem Answer - RF CafeDesign Problem

This circuit is an adaptation of the clamp gate, a circuit which is valuable in certain digital systems. The operation of the circuit shown in the following diagram should be self-explanatory.

Consider first only the part of the circuit drawn in solid lines. Its operation is perfectly straightforward, except in one case. Suppose that switch B is closed, and switch A is in the OFF position. Switch A is now thrown to ON. Since A is not make-before-break, there will be an instant where the relay is not energized, and could possibly drop out. This condition, which prevents correct operation of the circuit, is known as "static hazard." In this case, there would find that a slow-release relay would be considerably more expensive than the dpst type.

 

Full-Time Stereo

The input was able to pick up the 38-kc signal radiated by the output, thus making an oscillator out of the doubler, because T1 had been tuned to 38 kc instead of 19 kc! Detuning T1 from the maximum, I found a smaller, second "maximum," and then the tuner worked perfectly.

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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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