G2 · Published 21 September 2026 · By The Ham Desk

Power Supplies, Test Gear and the Art of Troubleshooting

The General class circuit questions are mostly about what is inside the box and what to do when the box stops working. This unit covers rectification and regulation, the instruments that tell you what is happening, and the safety habits that keep a repair from becoming an accident.

Band none
Study time 17
Level Core
questions 10

Waveform and antenna diagram for Circuits, Components and Measurements — Circuits, Components and Measurements — waveform overlay and radiation pattern

Pre-flight briefing

From the mains to the rail

A power supply does three jobs in sequence. First it transforms the mains down to a lower AC voltage. Then it rectifies: a single diode gives half-wave rectification, producing pulses at the mains frequency, while a bridge of four diodes gives full-wave rectification with pulses at twice the mains frequency and uses the whole transformer winding. Finally it filters, and a large capacitor across the output charges to the peak of each pulse and discharges into the load between pulses, leaving a small ripple.

Regulation is the fourth job and the one that matters most for radio: a regulator holds the output voltage steady as the load current changes, because a transmitter that draws 20 amperes on voice peaks will pull an unregulated supply down by several volts and produce chirp and distortion. Bleeder resistors across the filter capacitors serve a different purpose - they discharge the stored energy when the supply is switched off, which is a safety feature rather than a performance one.

Amplifiers, oscillators and logic

An amplifier stage takes a small signal and produces a larger copy, powered by the DC supply; the extra energy comes from the supply, not from the input. An oscillator is an amplifier with enough in-phase feedback that it sustains itself without any input - which is why an oscillator's output appears the moment power is applied and why a misbehaving amplifier can turn into one.

Digital circuits work with only two states, and the basic gates implement the logic: an AND gate outputs high only when all inputs are high, an OR gate when any input is high, and a NOT gate inverts. Flip-flops store a bit, and counters chain them to divide frequency - which is how a synthesised transceiver derives dozens of bands from one reference crystal.

Instruments, and the safety habit

A multimeter measures voltage in parallel with the circuit, current in series with it, and resistance with the circuit de-energised; connecting an ammeter across a supply is a short circuit, and connecting an ohmmeter to a live circuit gives a meaningless reading and often destroys the meter. An oscilloscope shows the waveform in the time domain, which is how you see distortion, ripple or a signal that is present but at the wrong level. A dummy load lets you test a transmitter into a known 50 ohm non-radiating load instead of into the antenna.

The safety habit that matters most concerns high voltage: the filter capacitors in a tube-type linear amplifier can hold a lethal charge for minutes after the supply is switched off and unplugged, because there is no load to drain them. Before reaching inside, switch off, unplug, and then short the capacitor terminals to the chassis with an insulated tool - and treat any circuit above about 50 volts as live until you have proved otherwise.

Terms you must be able to define
Term	What the examiner wants to hear
Rectifier	A diode circuit that converts alternating current into pulsating direct current.
Ripple	The residual AC variation on a DC supply output after filtering.
Regulator	A circuit that holds output voltage constant as load current varies.
Bleeder resistor	A resistor across a supply's output that discharges the filter capacitors when power is removed.
Dummy load	A 50 ohm non-radiating load used for testing transmitters.

Question deck 10 questions

G2B01 Recall

What does a rectifier do in a power supply?

G2B02 Core

How does a bridge rectifier differ from a single-diode rectifier?

G2B03 Core

What is the function of the filter capacitor in a power supply?

G2B04 Core

What is the purpose of a bleeder resistor across a power supply's filter capacitors?

G2B05 Core

What does a voltage regulator do?

G2B06 Core

How should a multimeter be connected to measure the current drawn by a circuit?

G2B07 Core

What is an oscilloscope most useful for when troubleshooting a transmitter?

G2B08 Stretch

Why is a dummy load used instead of an antenna when testing a transmitter?

G2B09 Stretch

What is the most likely cause of a fuse that blows immediately each time it is replaced?

G2B10 Stretch

Why can the filter capacitors in a high-voltage supply be dangerous even after the equipment is switched off and unplugged?

Reference sheet

The explanations for all ten questions sit on this sheet. Pick an answer on the left and the matching card lights up.

G2B01 Explanation 1

Key A — It converts alternating current into pulsating direct current

Rectification is the first step after the transformer, done by one diode for half-wave or four in a bridge for full-wave. The output is not yet smooth - it pulses - and the filter and regulator stages that follow are what turn it into usable DC.

Rule Fundamentals - rectifiers

G2B02 Explanation 2

Key D — It uses both halves of the AC cycle, giving pulses at twice the input frequency

Four diodes steer both halves of the cycle to the output in the same direction, so the ripple frequency doubles and less filtering is needed for the same result. A single diode discards half the cycle entirely, which is why half-wave supplies are found only in low-current applications.

Rule Fundamentals - full-wave rectification

G2B03 Explanation 3

Key C — It charges to the peak of each rectified pulse and discharges into the load between pulses, reducing ripple

The capacitor acts as a reservoir: it fills quickly during each pulse and empties slowly into the load, so the output sags only slightly between pulses. Larger capacitance or heavier load current both change how much the voltage sags, which is why a supply that is quiet on receive may hum on transmit.

Rule Fundamentals - power supply filtering

G2B04 Explanation 4

Key B — It discharges the capacitors when the supply is switched off, for safety

Without a discharge path, a large capacitor can hold a dangerous voltage for minutes after the supply is turned off and unplugged. Because a bleeder is a safety device, a supply that has lost its bleeder is more dangerous than one that never had a high-voltage section at all.

Rule 47 CFR §97.13(a) - safe working practice

G2B05 Explanation 5

Key A — It holds the output voltage steady as the load current or input voltage varies

Regulation is what keeps a transmitter's output stable between receive and the voice peaks of transmit, when current demand can jump by an order of magnitude. An unregulated supply sags under that load, and the sag shows up as chirp, distortion or a power output that falls on peaks.

Rule Fundamentals - regulation

G2B06 Explanation 6

Key D — In series with the circuit, so the current flows through the meter

Current measurement requires the meter to be part of the current path, which means breaking the circuit and inserting the meter in series. Connecting it in parallel across a supply puts a near-short across the source and usually destroys the meter's internal fuse or the meter itself.

Rule Fundamentals - measurement technique

G2B07 Explanation 7

Key C — Showing the shape of the waveform, revealing distortion, ripple or incorrect level

An oscilloscope is a time-domain instrument: it shows you what the signal looks like, which is exactly what you need to see flat-topping, hum on the envelope or a stage that is passing no signal at all. Frequency measurement and SWR need different instruments.

Rule Fundamentals - test equipment

G2B08 Explanation 8

Key B — It presents a known 50 ohm load and radiates almost nothing, so tests do not interfere with anyone

A dummy load gives you a stable, known impedance so that any problem you find is the transmitter's, not the antenna's - and because it converts the power to heat instead of radiation, you can test at full power without occupying the band or causing interference.

Rule 47 CFR §97.101(d) - avoiding interference

G2B09 Explanation 9

Key A — A short circuit or excessive current demand somewhere in the circuit

A fuse blows because current exceeded its rating, and instant failure on replacement means the overload is permanent, not intermittent. Replacing it with a larger fuse or a bolt converts a cheap failure into an expensive one - the fault has to be found.

Rule 47 CFR §97.13(a) - safe equipment practice

G2B10 Explanation 10

Key A — They store charge and, without a discharge path, may hold a lethal voltage for minutes

A capacitor is an energy store, and with no load across it the charge simply sits there. The safe procedure is to switch off, unplug, wait, and then short the capacitor terminals to the chassis with an insulated tool before touching anything inside.

Rule 47 CFR §97.13(a) - working on high-voltage equipment

How to use this unit

Work the ten questions in one sitting with the reference sheet covered, then uncover it and read every explanation - including the ones you got right. The wording of the real exam is different, so learn the reasoning rather than the answer letters.