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# What's Your EQ?March 1964 Radio-Electronics

 March 1964 Radio-Electronics [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.

Seeing a reader name of Qutaiba Bassim El-Dhuwaib would not seem unusual in one of today's technical magazines, but having it appear in a 1964 issue of Radio-Electronics was definitely a rarity. Such was the case with this first "Black Box" circuit challenge submitted by the aforementioned subscriber. I took a WAG at the answer and got it right, but without considering the theory behind it. Fortunately, Mr. El-Dhuwaib provides that gory detail for us. It is a pretty clever scheme for effecting a phase shift while not affecting the magnitude. Such circuits were probably more intuitive to designers in the days of analog. The second mystery circuit requires being familiar with types of meter movements commonly used in DC and AC voltmeters. Having begun in the craft prior to the advent of digital multimeters (that includes me) helps. If you have never dealt with vacuum tube circuits, you probably won't have much luck with the last circuit. I worked on a couple tube-based radars whilst in the USAF in the late 1970s to early 1980s, and managed to remember enough about the operation to guess the answer correctly.

## What's Your EQ?

Always Half

An ac generator is connected to a network consisting of two resistors, R and RV, and the black box shown in the diagram. It is found that the voltage between A or B is independent of the value of RV. Whether RV is shorted or open, the voltage across AB is E/2 where E is the voltage of the generator. It is also independent of the frequency. Why?

- Qutaiba Bassim El-Dhuwaib

What Voltage?

Three voltmeters are connected as shown. V1 is an electrostatic type, calibrated to read peak voltage values. It indicates that the output from the rectifier is 1,000 peak volts. V2 is a dc voltmeter of the d'Arsonval type. V3 is an ac voltmeter of the electrodynamometer or iron-vane type. What will be the voltage indicated by voltmeters V2 and V3?

- Kendall Collins

A Distorted Puzzler

This could be any voltage amplifier stage - most likely audio. Could also be a triode. Signal is getting through, but with less than usual volume and with considerable distortion. The tube is good, the voltages are as shown. The components? Well, better check 'em. Won't have to disconnect anything to find any bad ones, though. Just look.

- Jack Darr

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.

 RF Cafe Quizzes RF Cafe Quiz #71: Tech Headlines for Week of 3/13/2023 RF Cafe Quiz #70: Analog & RF Filter Basics RF Cafe Quiz #69: RF Electronics Basics RF Cafe Quiz #68: RF & Analog Company Mergers & Acquisitions in 2017 RF Cafe Quiz #67: RF & Microwave Company Name Change History RF Cafe Quiz #66: Spectrum and Network Measurements RF Cafe Quiz #65: Troubleshooting & Repairing Commercial Electrical Equipment RF Cafe Quiz #64: Space-Time Adaptive Processing for Radar RF Cafe Quiz #63: Envelope Tracking Power Amplifiers RF Cafe Quiz #62: Stimson's Introduction to Airborne Radar RF Cafe Quiz #61: Practical Microwave Circuits RF Cafe Quiz #60: Ten Essential Skills for Electrical Engineers RF Cafe Quiz #59: Microwave Circulator Design RF Cafe Quiz #58: Microwave and Millimeter-Wave Electronic Packaging RF Cafe Quiz #57: Frequency-Agile Antennas for Wireless Communications RF Cafe Quiz #56: Tube Testers and Electron Tube Equipment RF Cafe Quiz #55: Conquer Radio Frequency RF Cafe Quiz #54: Microwave Mixer Technology and Applications RF Cafe Quiz #53: Chipless RFID Reader Architecture RF Cafe Quiz #52: RF and Microwave Power Amplifiers RF Cafe Quiz #51: Antennas and Site Engineering for Mobile Radio Networks RF Cafe Quiz #50: Microstrip Lines and Slotlines RF Cafe Quiz #49: High-Frequency Integrated Circuits RF Cafe Quiz #48: Introduction to Infrared and Electro-Optical Systems RF Cafe Quiz #47: LCP for Microwave Packages and Modules RF Cafe Quiz #46: RF, Microwave, and Millimeter-Wave Components RF Cafe Quiz #45: Dielectric and Thermal Properties of Materials at Microwave Frequencies RF Cafe Quiz #44: Monopulse Principles and Techniques RF Cafe Quiz #43: Plasma Antennas RF Cafe Quiz #42: The Micro-Doppler Effect in Radar RF Cafe Quiz #41: Introduction to RF Design Using EM Simulators RF Cafe Quiz #40: Introduction to Antenna Analysis Using EM Simulation RF Cafe Quiz #39: Emerging Wireless Technologies and the Future Mobile Internet RF Cafe Quiz #38: Klystrons, Traveling Wave Tubes, Magnetrons, Crossed-Field Amplifiers, and Gyrotrons RF Cafe Quiz #37: Component Reliability for Electronic Systems RF Cafe Quiz #36: Advanced RF MEMS RF Cafe Quiz #35: Frequency Synthesizers: Concept to Product RF Cafe Quiz #34: Multi-Gigabit Microwave and Millimeter-Wave Wireless Communications RF Cafe Quiz #33: Battlespace Technologies: Network-Enabled Information Dominance RF Cafe Quiz #32: Modern Communications Receiver Design and Technology RF Cafe Quiz #31: Quantum Mechanics of Nanostructures RF Cafe Quiz #30: OFDMA System Analysis and Design RF Cafe Quiz #29: Cognitive Radar RF Cafe Quiz #28: Human-Centered Information Fusion RF Cafe Quiz #27: Remarkable Engineers RF Cafe Quiz #26: Substrate Noise Coupling in Analog/RF Circuits RF Cafe Quiz #25: Component Reliability for Electronic Systems RF Cafe Quiz #24: Ultra Low Power Bioelectronics RF Cafe Quiz #23: Digital Communications Basics RF Cafe Quiz #22: Remember the Basics? RF Cafe Quiz #21: Wireless Standards Knowledge RF Cafe Quiz #20: Famous First Names RF Cafe Quiz #19: Basic Circuit Theory RF Cafe Quiz #18: Archaic Scientific Words & Definitions RF Cafe Quiz #17: Inventors & Their Inventions RF Cafe Quiz #16: Antennas RF Cafe Quiz #15: Numerical Constants RF Cafe Quiz #14: Oscillators RF Cafe Quiz #13: General Knowledge RF Cafe Quiz #12: Electronics Corporations Headquarters RF Cafe Quiz #11: Famous Inventors & Scientists RF Cafe Quiz #10: A Sampling of RF & Wireless Topics RF Cafe Quiz #9: A Smorgasbord of RF Topics RF Cafe Quiz #8: Hallmark Decades in Electronics RF Cafe Quiz #7: Radar Fundamentals RF Cafe Quiz #6: Wireless Communications Fundamentals RF Cafe Quiz #5: Company Logo Recognition RF Cafe Quiz #4: General RF Topics RF Cafe Quiz #3: General RF/Microwave Topics RF Cafe Quiz #2: General RF Topics RF Cafe Quiz #1: General RF Knowledge Vacuum Tube Quiz, February 1961 Popular Electronics Kool-Keeping Kwiz, June 1970 Popular Electronics Find the Brightest Bulb Quiz, April 1960 Popular Electronics Where Do the Scientists Belong? - Feb 19, 1949 Saturday Evening Post Vintage Electronics Magazine Quizzes Quiz on AC Circuit Theory, December 1970 Popular Electronics Magnetic Phenomena Quiz, February 1962 Popular Electronics Electronics Geography Quiz, April 1970 Popular Electronics Electronic Menu Quiz, August 1963 Popular Electronics Electronic Noise Quiz, August 1962 Popular Electronics Electronic Current Quiz, October 1963 Popular Electronics Electronic Inventors Quiz, November 1963 Popular Electronics Resistor Function Quiz, January 1962 Popular Electronics Electronic Measurement Quiz, January 1963 Popular Electronics Vintage Electronics Magazine Quizzes What's Your EQ?  - March 1964 Radio-Electronics What's Your EQ?  - April 1962 Radio-Electronics What's Your EQ? - May 1962 Radio-Electronics What's Your EQ? - June 1962 Radio-Electronics What's Your EQ? - April 1967 Radio-Electronics What's Your EQ? - March 1967 Radio-Electronics What's Your EQ? - December 1964 Radio-Electronics What's Your EQ? - January 1967 Radio-Electronics Wanted: 50,000 Engineers - January 1953 Popular Mechanics What's Your EQ? - August 1964 Radio-Electronics Voltage Quiz - December 1961 Popular Electronics What is It? -  June 1941 Popular Science What Do You Know About Resistors? - April 1974 Popular Electronics What's Your EQ? - September 1963 Radio-Electronics Potentiometer Quiz - September 1962 Popular Electronics Mathematical Bafflers - March 1965 Mechanix Illustrated Op Amp Quiz - October 1968 Popular Electronics Electronic "A" Quiz - April 1968 Popular Electronics What's Your EQ? - May 1961 Radio-Electronics Popular Science Question Bee - February 1939 Popular Science What is It? - A Question Bee in Photographs - June 1941 Popular Science What's Your EQ? - June 1961 Radio-Electronics What's Your EQ? - June 1964 Radio-Electronics What's Your EQ? - May 1964 Radio-Electronics What's Your EQ? - August 1963 Radio-Electronics What's Your EQ? - May 1963 Radio-Electronics Bridge Function Quiz - September 1969 Radio-Electronics What's Your EQ? - March 1963 Radio-Electronics What's Your EQ? - February 1967 Radio-Electronics Circuit Quiz - June 1966 Radio-Electronics What's Your EQ? - June 1966 Radio-Electronics Electronics Mathematics Quiz - June 1969 Popular Electronics Brightest Light Quiz - April 1964 Popular Electronics What's Your EQ? - April 1963 Radio-Electronics Electronics "B" Quiz - July 1969 Popular Electronics Ohm's Law Quiz - March 1969 Popular Electronics Antenna Quiz - November 1962 Electronics World Color Code Quiz - November 1967 Popular Electronics CapaciQuiz - August 1961 Popular Electronics Transformer Winding Quiz - December 1964 Popular Electronics Audiophile Quiz - November 1957 Radio-electronics Capacitor Function Quiz - March 1962 Popular Electronics Greek Alphabet Quiz - December 1963 Popular Electronics Circuit Designer's Name Quiz - July 19680 Popular Electronics Sawtooth Sticklers Quiz - November 1960 Radio-Electronics Elementary Radio Quiz - December 1947 Radio-Craft Hi-Fi Quiz - October 1955 Radio & Television News Electronics Physics Quiz - March 1974 Popular Electronics A Baffling Quiz - January 1968 Popular Electronics Electronics IQ Quiz - May 1967 Popular Electronics Plug and Jack Quiz - December 1967 Popular Electronics Electronic Switching Quiz - October 1967 Popular Electronics Electronic Angle Quiz - September 1967 Popular Electronics International Electronics Quiz - July 1967 Popular Electronics FM Radio Quiz - April 1950 Radio & Television News  Bridge Circuit Quiz -December 1966 Popular Electronics Diode Function Quiz - August 1965 Popular Electronics Diagram Quiz, August 1966 Popular Electronics Quist Quiz - November 1953 QST TV Trouble Quiz, July 1966 Popular Electronics Electronics History Quiz, December 1965 Popular Electronics Scope-Trace Quiz, March 1965 Popular Electronics Electronic Circuit Analogy Quiz, April 1973 Test Your Knowledge of Semiconductors, August 1972 Popular Electronics Ganged Switching Quiz, April 1972 Popular Electronics Lamp Brightness Quiz, January 1969 Popular Electronics Lissajous Pattern Quiz, September 1963 Popular Electronics Electronic Quizoo, October 1962 Popular Electronics Electronic Photo Album Quiz, March 1963 Popular Electronics Electronic Alphabet Quiz, May 1963 Popular Electronics Quiz: Resistive? Inductive? or Capacitive?, October 1960 Popular Electronics Vector-Circuit Matching Quiz, June 1970 Popular Electronics Inductance Quiz, September 1961 Popular Electronics RC Circuit Quiz, June 1963 Popular Electronics Diode Quiz, July 1961 Popular Electronics Electronic Curves Quiz, February 1963 Popular Electronics Electronic Numbers Quiz, December 1962 Popular Electronics Energy Conversion Quiz, April 1963 Popular Electronics Coil Function Quiz, June 1962 Popular Electronics Co-Inventors Quiz - January 1965 Electronics World "-Tron" Teasers Quiz - October 1963 Electronics World Polarity Quiz - March 1968 Popular Electronics Television I.Q. Quiz - October 1948 Radio & Television News Amplifier Quiz Part I - February 1964 Popular Electronics Semiconductor Quiz - February 1967 Popular Electronics Unknown Frequency Quiz - September 1965 Popular Electronics Electronics Metals Quiz - October 1964 Popular Electronics Electronics Measurement Quiz - August 1967 Popular Electronics Meter-Reading Quiz, June 1966 Popular Electronics Electronic Geometry Quiz, January 1965 Popular Electronics Electronic Factor Quiz, November 1966 Popular Electronics Electronics Math Quiz, November 1965 Popular Electronics Series Circuit Quiz, May 1966 Popular Electronics Electrochemistry Quiz, March 1966 Popular Electronics Biz Quiz: Test Your Sales Ability - April 1947 Radio News Electronic Analogy Quiz, November 1961 Popular Electronics Electronic Coupling Quiz, August 1973 Popular Electronics Electronics Analogy Quiz, August 1960 Popular Electronics Audio Quiz, April 1955 Popular Electronics Electronic Unit Quiz, May 1962 Popular Electronics Capacitor Circuit Quiz, June 1968 Popular Electronics

These are the answers. This month's puzzles are on, page 37. 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.

Fig. 1 - Black Box contents.

Fig. 2 - Black Box vector voltages

Always Half

The black box contains a capacitor and a resistor equal to R as in Fig. 1. The voltage ECA = EAD = E/2 having zero angle with E; the voltage EBC is 90° out of phase with EBD, and the vector sum is equal to E: consider the modified vector diagram (Fig. 2). EBC is always perpendicular to EBD, thus point B will fall on the circumference of a circle having a diameter of E or a radius of E/2. Likewise, as point A falls in the center of this circle, the distance between A and B will become E/2. Whatever the resistance, only the phase shift will change.

This circuit is used often as a phase shifter to change phase without changing amplitude.

Note: This puzzle, in slightly different form, was published as "Output Voltage" by Cameron McCulloch in the October 1963 issue and evoked a flood of disbelieving letters as well as criticisms of an attempted abridged mathematical proof (Mr. McCulloch's proof was much longer than the one printed).

Readers may be assured that the circuit is "bench-tested," that it works, and is indeed so ruggedly based in theory that an unfortunate change of sign in one of the terms of the October explanation did not change the final result.

What Voltage?

The output from the full-wave rectifier consists of negative half-cycles at the rate of 800 per second. Therefore the output is negative with respect to the center tap on the transformer secondary.

Unless otherwise stated, dc voltmeter readings should be taken as average values, and ac voltmeter readings should be taken as rms values. Observing polarity, the dc voltmeter (V2) reading is 636 volts, determined by multiplying 0.636 times the peak value of 1,000 volts. The ac voltmeter (V3) reading is 707 volts, determined by multiplying 0.707 times the peak value of 1,000 volts.

If ac voltmeter V3 is a basic d'Arsonval type, calibrated with and using a half-wave rectifier, the indicated voltage will be entirely different. This method is used in some vom instruments. Again observing polarity, the meter would indicate 1,414 volts, or double the rms value, in the forward position and zero volts with the test leads reversed. The output waveform of the circuit shown in the puzzler, along with the relative voltages, is shown in the diagram. The 0.636 factor applies to the average value of a sine wave and also to the output of an unfiltered full-wave rectifier.

A Distorted Puzzler

A simple one, and not uncommon. The key is, of course, that 6 volts positive at the grid, which causes a high plate current and a low plate voltage. Pretty obviously, the 0.01-μf input coupling capacitor is leaking badly.

Posted July 5, 2024