125 Transistor Projects - Rufus Turner

125 Transistor Projects - Rufus Turner - What are "choke" filters?

Reading time: 3 minute

Did you know that ...? In electronics, a "choke" is an inductor used to block high frequencies when passing direct current (DC) and low frequencies when passing alternating current (AC) in an electrical circuit? A "choke" usually consists of an insulated coil of wire often wound around a magnetic or ferrite core.

What does the book present?

Cele 125 circuits with a single transistor presented in this book are useful for amateur electronics and more. Only a few examples of cheap transistors are used in the book; however, all types are represented: germanium, silicon, NPN, PNP, junction and FET. The reader should be able to configure and test these circuits with minimal effort and equipment.

Circuit designs take into account the relatively wide spread of transistor values; the typical values ​​of the manufacturers were used (or where only the maximum and minimum values ​​were specified, the minimum value was used).

Thus, where there is a specified 30K resistor, a choice between standard 27K and 33K EIA values ​​may be indicated and it may be necessary to try both values ​​to determine which works best. However, in the case of frequency-determining RC networks, the exact values ​​displayed must be used. Following these instructions, the reader should have little trouble duplicating or improving the desired performance.

These circuits are offered to the student who wants to configure and test typical circuits with their own instructions, to the designer who wants functional blocks ready to be incorporated in a system and to the hobbyist whose amateur interests will be served by preset, pre-tested circuits.

The structure of the book


Germanium common - emitter amplifier
Silicon common - emitter amplifier
Degenerative common - emitter amplifier
Transformer - coupled common - emitter amplifier
FET Common - source amplifier
Emitter follower (biased divider)
Emitter follower (biased resistor)
FET source follower
Headphone amp
Microphone handle preamplifier
Driver for Class B stage
Five-watt power amplifier
Phase inverter
Audio mixer
Gated amplifier
Tuned - transformer bandpass amplifier
Inductor - capacitor - tuned bandpass amplifier
Inductor - capacitor - tuned bandstop amplifier
RC - tuned bandpass amplifier
RC - tuned bandstop amplifier


Broadcast band RF amplifier (preselector)
Conventional 455 kHz IF amplifier
Single - tuned 455 kHz IF amplifier
FET 455 kHz IF amplifier
DC voltage amplifier
DC current amplifier (low-level type)
DC current amplifier (power type)
Wideband (video) amplifier
DC source follower
DC emitter follower


Transformer - tuned AF oscillator (PNP)
Transformer - tuned AF oscillator (FET)
Hartley - Type AF oscillator
Phase - shift RC audio oscillator
Light - operated AF oscillator
Self-excited RF oscillator
Conventional crystal oscillator
Pierce crystal oscillator
Multi-frequency crystal oscillator
Self-excited 100 - kHz oscillator
Crystal type 100 - kHz oscillator
Power AF oscillator
Beat frequency oscillator (BFO)
Micropower AF oscillator
Carrier - operated AF oscillator
Pulse - generating oscillator
Relaxation oscillator
TV sound - channel marker oscillator
Self-modulated RF oscillator


Sensitive DC relay (NPN)
Sensitive DC relay (PNP)
Sensitive DC relay (FET)
Heavy-duty DC relay
All-solid-state DC relay
AC / RF relay
Tuned AF relay
Photoelectric Relay (solar cell type)
Photoelectric relay (photofet type)
Heavy-duty photoelectric control (all solid-state)
Temperature - sensitive relay
Touch-plate relay
Relay coincidences
Coincidence switch ("and" circuit)
Inverter signal
Heater control (manual adjust)
Audible alarm
Visual alarm (lamp flasher)
Carrier - failure alarm
interval timer
Phase shifter


DC microammeter (NPN)
DC microammeter (PNP)
Electronic DC voltmeter
General-purpose field-strength meter
TV field-strength meter
Dip oscillator (PNP)
Dip Oscillator (FET)
Dip adapter
AF frequency meter
Audio signal injector
Step - type audio oscillator
Inductance / capacitance checker
LC charts
RF signal comparator
Static detector (electrometer)
Harmonic amplifier for frequency standards
Electronic load resistor (PNP)
Electronic load resistor (NPN)
Heterodyne frequency meter
AF signal-tracer adapter for VOM Phone monitor
Monitor CW
DC voltage calibrator
electronic thermometer
Sensitive absorption wavemeter
AF wattmeter
Tuned AF analyzer
Bright-bulb stroboscope
Sensitizer for DC milliammeter
Circle generator for oscilloscope wheel patterns


Variable DC power supply
DC voltage regulator (shunt type)
DC voltage regulator (series type)
DC to DC inverter (low voltage)
DC to DC inverter (medium voltage)
DC to DC inverter (high voltage)
DC supply for tunnel diodes
Constant current adapter (low level)
Constant current adapter (high level)
Electronic filter "choke"


Simple broadcast receiver
Diode receiver with transistor AF amplifier
Step-tuned broadcast receiver
Selective broadcast receiver
Regenerative broadcast receiver
All-wave regenerative receiver
Autodyne converter
Sun-powered broadcast receiver
Meter-type tuning indicator
Light-bulb type tuning indicator
CW transmitter
Frequency doubled
Light beam receiver
Oscillator practice codes


  1. Excellent book for beginners. You omitted the word 'One' in the name. It resembles "One transistor, two transistors" from the Cristal Collection (Ed. Albatros), but much "richer" in montages, of course.

  2. The word 'One' was omitted for a clearer title. It really looks like "One transistor, two transistors" written by Ilie Mihaescu.

  3. Yes, about the coil in the presentation, I found in the car radio, on the power supply, 2 meters of winding conductor of 0,5, put in two and wound on a ferrite bar, the question was why so, then I understood that it behaves as a blockage for alternative parasitic signals coming from the spark plug power supply.

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