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A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled
conductors — the transformer's coils or "windings". Except for air-core transformers, the conductors are commonly
wound around a single iron-rich core, or around separate but magnetically-coupled cores. A varying current in the
first or "primary" winding creates a varying magnetic field in the core (or cores) of the transformer. This varying
magnetic field induces a varying electromotive force (EMF) or "voltage" in the "secondary" winding. This effect
is called mutual induction. - Wikipedia
The following table represents the most common color coding for transformer leads.
| Primary Leads |
Black |
| If it is tapped: |
|
|
Common |
Black |
| Tap |
Black / Yellow |
| End |
Black / Red |
| High Voltage Winding |
Red |
| (center tap) |
Red / Yellow |
| Rectifier Filament Winding |
Yellow |
| (center tap) |
Yellow / Blue |
| Filament Winding #1 |
Green |
| (center tap) |
Green / Yellow |
| Filament Winding #2 |
Brown |
| (center tap) |
Brown / Yellow |
| Filament Winding #3 |
Slate |
| (center tap) |
Slate / Yellow |
| Plate Lead |
Blue |
| B+ Lead |
Red |
| Grid (or diode) Lead |
Green |
| A-V-C (or ground) Lead |
Black |
| Tuning Slug Color Codes |
| 455 kHz 1st IF |
Yellow |
| 455 kHz 2nd IF |
White |
| 455 kHz 3rd IF |
Black |
| 455 kHz Oscillator |
Red |
| 10 MHz 1st IF |
Green |
| 10 MHz 2nd IF 10 MHz 3rd IF |
Orange, Brown, or Black |
| Plate Lead, Primary |
Blue |
| B+ Lead, Primary (w/or w/o center-tap) |
Red |
| Plate Lead (center-tapped primary) |
Brown (or Blue*) |
| Grid Lead, Secondary |
Green |
| Grid Lead (center-tapped secondary) |
Yellow (or Green*) |
| Grid Return, Secondary |
Black |
* Push-pull only
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