[Amps] Note on paralelling transformers

[Will Matney]

I figured I might as well add this because home brew amps have used 
paralleled transformer in the past to either increase the voltage or the 
current. When connecting the transformer windings, they must be "in 
phase" with each other. Some transformers is hard to connect this way 
because the have two of the same color wires for each winding. If the 
transformers are connected "out of phase" they will buck each other. 
When this happens, you would get little or no output voltage and they 
would act like they were shorted. You will know when this happens 
believe me. You'll get a BIG hum and the fuse will open. Hopefully it 
wont damage the windings too! When winding transformers or ordering 
them, always have a different color wire for the start and stop of each 
winding. This way it is easy to keep them in phase with on another. On 
the schematics you'll see a black dot at one leg of each winding. This 
is put there so you will know the correct connection to keep it in 
phase. On transformers with the same color leads like two black wires 
for the primary, you will need to find which goes to the start and stop 
of each winding. For parallel operation the two starts tie together and 
the two stops. In series operation, you will have a start and stop 
together with the other two going to the line. Anyhow, I've wrote about 
all I can think of on this so have at it!

Will Matney
US Amp