Practical Circuits: Power Supplies, Amplifiers, Oscillators, and Troubleshooting
Power supplies
The chain is transformer, rectifier, filter, regulator. A half-wave rectifier produces ripple at the line frequency and needs a large filter; full-wave and bridge rectifiers produce ripple at twice line frequency, which is easier to filter. Ripple falls as filter capacitance and load resistance increase. Zener shunt regulators are simple but inefficient; series-pass linear regulators are quiet; switching regulators are efficient but generate RF noise, a real clue when a receiver hums or a band is noisy.
Amplifiers
Class A conducts 360 degrees: linear but inefficient. Class AB is the usual audio compromise. Class B conducts 180 degrees per device. Class C conducts far less than 180 degrees: efficient but usable only with a tuned output, as in FM and CW stages. Bias faults show up as distortion, excessive current, or thermal runaway.
Oscillators
Every oscillator needs gain, positive feedback, and a frequency-determining network. Colpitts splits the capacitance, Hartley splits the inductance, and Pierce places a crystal in a pi network. Crystals trade tuning range for stability; a phase-locked loop multiplies a stable reference and provides programmable channel steps.
Troubleshooting
Measure voltages before suspecting components. No output with correct supply voltages points to the stage, not the supply. Half the expected collector voltage suggests an open bias resistor; full supply voltage at the collector suggests a shorted device. Always test a transmitter into a dummy load, never into an open antenna.
Rule of thumb: on a 60 Hz line, full-wave ripple appears at 120 Hz and half-wave ripple at 60 Hz.