Power conversionRebuild shelfUnplug and unscrew

Ferrite core

Also called ferrite bead, clip-on choke, AM rod, flyback core.

The clip-on cylinder on a cable, the rod in an AM radio, the cores in a supply. Useful as common-mode noise suppression and as material for people who wind their own. The mix number is almost never known on salvage.

If you are new to this category

These parts change wall power into the lower voltage a device uses. A sealed supply with a label is the safer kind. An open board from a lamp can still be connected to the wall on the side that looks like low voltage. Isolated means the output is not electrically connected to the wall. If you are not sure, treat the output as live.

Read the label out loud: volts, amps, and the polarity symbol. Then measure. A number you remember from a similar brick is not a measurement.

A sealed supply versus an open board

Left: a brick. The label is your spec, and the plastic is the safety barrier. Right: a board taken out of a lamp or a charger. Unless you have checked that the output is isolated from the prongs, do not let it touch a project you will handle while it is plugged in.

Sheet metal and glass. Case steel, shattered platters, lamp glass, and magnet chips cut deeper than they look.

Specification. The right-hand column is what is typical. The label on the part in your hand wins if they disagree.
What to look for	Usual figure
Cable bead	Slips over a lead. More turns is more impedance, until the core saturates.
AM rod	A long ferrite used as an antenna. Fragile.
Unknown mix	Fine for a noise bead. A guess for a power transformer.

Volts are electrical pressure, amps are how much current is flowing, and ohms are how hard the part resists that flow. A higher voltage than the part was built for is how salvage parts die on the bench. If a cell in the table says “read the stamp”, that stamp is the whole specification.

What people actually use it for

Noise on a long lead
A winding exercise
Keeping, because you will want one later

Leave this one when

The core is cracked. A cracked ferrite does not behave, and the edges are sharp.

Buying a new one is the better idea when

A catalog core with an AL value, when the inductance has to come out right.

How to tell if this one still works

No electrical test required for a clip-on. For a wound choke, see inductors.

Tools you will want: Hands.

Words on this page

Short meanings, so the rest of the entry is readable if you are not already doing this every weekend.

transformer: Two coils on an iron core. It changes voltage and, in a proper one, isolates the output from the wall. Heavy old adapters are this. Microwave oven transformers are a different, dangerous kind.

Where people actually find it

2 notes, most useful first. “Leave it” means the part is in that machine and you should not take it: it is dangerous, worn out, or only useful if you already know that exact repair.

Harvest at a glance
From	Call	How many	How often	Where it sits
Clock radio or stereo	Worth it	1	usually	AM radio.
Wall adapter	Bonus	1	usually	On the cord.

Worth pullingClock radio or stereo1 · usually
In this particular machine
A ferrite rod antenna.
Where to look
AM radio.
How to get it out
Fragile.
The condition to expect
Good if unbroken.
Bonus, if you are already in thereWall adapter1 · usually
In this particular machine
A clip-on or molded bead.
Where to look
On the cord.
How to get it out
Slide it off.
The condition to expect
Good.