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What's Your EQ?
March 1962 Radio-Electronics

March 1962 Radio-Electronics

March 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.

Three more "What's Your EQ?" challenges were presented in the March 1962 issue of Radio Electronics magazine. Two were submitted by readers, and one was provided by columnist Jack Darr. I've said before that I believe Jack is used as a fill-in when not enough readers provide good content. Jack's circuits always pertain to television, since that is his column's main topic. You are excused if you decide to not attempt to "troubleshoot" it, or try and get it wrong. The other two should be within the ability of most RF Cafe visitors to figure out. As I have pointed out in the past, the first thing to do when a series-parallel circuit is given is to determine whether it can be redrawn in a manner that results in a more recognizable configuration - like a bridge or something with symmetry - and rearranging component positions and uncrossing lines. Do that for the "Applied Voltage" problem. "What's the Component" is pretty clever.

What's Your EQ?

What's Your EQ?, March 1962 Radio-Electronics - RF CafeIt's stumper time again. Here are three little beauties that will give you a run for the money. They may look simple, but double-check your answers before you say you've solved them. For those that get stuck, or think that it just can't be done, see the answers next month. If you've got an interesting or unusual answer send it to us. 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). Also, we're in the market for puzzlers and will pay $10 and up for each one accepted. Write to EQ Editor, Radio-Electronics, 154 West 14th St., New York, N. Y.

For answers to last month's puzzle see page 73.

Waveform found on pin 2 and pin 4 of Du Mont horizontal oscillator - RF Cafe

Fig. 2 - Waveform found on pin 2 and pin 4 of Du Mont horizontal oscillator. Looks as if there is something wrong here, what? Too many wiggles for the number of spikes!

Schematic of Du Mont RA-166 horizontal oscillator section - RF Cafe

Fig. 1 - Schematic of Du Mont RA-166 horizontal oscillator section.

Half Speed TV

The horizontal oscillator wouldn't lock in, or come anywhere near it. Some previous "technician" (Ha!) had tied pins 5 and 2 of the 6AL5 together! Apparently this brought the oscillator somewhere within range, but she sure didn't hold for long. Under the test conditions shown in Fig. 1 (ringing coil strapped out, sync grounded), the waveform shown in Fig. 2 was found on pins 2 and 4 of the 6SN7 horizontal oscillator. All dc voltages were exactly as shown on the schematic!

From the fact that the oscillator would make a dual picture on the screen, it was obviously running at exactly half-speed (7875 cycles), but why? Doesn't it seem that a defective part such as a leaky capacitor or drifted resistor anywhere in the waveshaping circuits would affect the dc voltages?

  - Jack Darr

Two voltmeters were hooked across the circuit and the readings shown were obtained - RF CafeApplied Voltage

Here is a simple series circuit. Two voltmeters were hooked across the circuit and the readings shown were obtained. What is the applied voltage (Ea) ?

  - John M. Resch

What's the Component?

An impoverished experimenter owns only a voltohmmeter, no other test equipment. He is about to check continuity on a valuable thermistor when he recalls that if more than 2 volts are applied the thermistor will burn out. He does not know the battery voltages used on the resistance ranges of the meter. Rather than open his meter, he picks up a common electrical component and with it determines whether it is safe to apply the thermistor directly to the meter leads. What is the component? (It is not a resistor.)

  - Richard P. Jones

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

One wiggle per spike - RF Cafe

This is what it ought to look like! One wiggle per spike. This happens to be the one shown on the schematic, too!

Waveform found on plate of Du Mont horizontal oscillator - RF Cafe

Waveform found on plate of Du Mont horizontal oscillator, pins 2 and 4. Too many wiggles for the number of spikes! Last month we showed you the correct waveform by mistake. (See Mar., p. 57).

Half Speed TV

It sure does look as though a defective part should affect the dc voltages. However, R304, the 220,000-ohm resistor in the "output" plate of the 6SN7 multivibrator measured almost exactly 470,000 ohms instead of the normal 220,000! This was changing the time constant of that circuit so that the oscillator ran at half-speed. What about the dc voltages? We replaced the defective resistor and measured again, just to be certain: with either a good resistor or the bad one, we still got 120 volts on that plate, using a vtvm.

Explanation: due to the very small fraction of the time that this plate is conducting, the voltage drop (dc) was not enough to show up! However, with these symptoms, and with the oscillator operating under the conditions given, there are only nine parts, maximum, that could conceivably affect the operating frequency! We are assuming that the tube was changed first, which it was. It must be one of the few parts left in the circuit, and it was.

 

Therefore the voltage dropped across R3 and R4 will equal the voltage dropped across R4, R5 and R6 - RF CafeApplied Voltage

R3 equals R5 + R6, and will drop the same voltage. Therefore the voltage dropped across R3 and R4 will equal the voltage dropped across R4, R5 and R6. Thus it is clear that Ea is 45 volts.

 

What's the Component?

The component is an electrolytic (or other high-capacitance) capacitor. With the meter set for resistance, he charges the capacitor. He then switches to read voltage, and reads the voltage on the capacitor. This gives the internal battery voltage of the resistance range to which the meter was set.
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About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

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...

Copyright  1996 - 2026

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