Transformer wire colour? red/yellow

[ValveBytes]

I found an old transformer in a hammond type organ looks like a vintage fender type, anyway it has a wire on it that is red/yellow stripped? what is that wire for?

the other wires are:
Black: AC primary
Red: 310/310 sec
Yellow: 3.15/3.15 sec
Green/Yellow stripe: Ground

and then this red/yellow wire that I think I remember measuring 100v on?

transformer is lay down type with cloth covered wires marked: A0-28335-3 606419 it was running 9! valves 1x EZ81, 2xEL84, 2x7247, 2x12AX7 and 2xEF86

I'll be using it in a 5E3 type amp

[Enzo]

The red and red are the high voltage windings, and they should be wired to your rectifier tube. The red/yellow wire will be the center tap of that winding, and usually it would go to ground. In some circuits, they might run this red/yellow wire to a standby switch, and then to ground.