weird question about OT wiring

[electric]

Just hit my mind don't know if it is covered before...

can someone wire a push pull tranny like single ended by using the centre tap and the other two taps of the primary wired together?

will it harm the OT? will the impedance ratio go down by half? what about wattage rating?

[Structo]

Well depending on the OT, I think you would be better suited to use the two secondary wires and not use the center tap.

I'm sure someone else will chime in about this that has done it.

[paulster]

You'd actually use the two ends of the winding and tape off the centre tap for this purpose, which will then of course change the impedance ratio.

However, push-pull transformers are generally not suitable for single-ended use because of their construction (i.e. not air-gapped). You can have all sorts of core saturation related nasties when using them that wouldn't occur in push-pull mode because the DC bias is cancelled out between both halves of the winding.

With a big PP transformer in a small SE amp you'll probably get it to work okay though, but you generally need to use a transformer designed for single-ended use.

[electric]

cool thanks for the replies guys

i just have one 10w 20k p-p OT sitting and thought about it...

[VacuumVoodoo]

You can not do it. It'll be equivalent to parallel connection of two (almost) identical coils wound in opposite directions. Result will be combined winding inductance = 0 i.e. short circuit for anything other than DC current and no magnetic flux in the core for AC.

To use PP OT in SE circuit with moderate success is to build a PP amp, bias it to class A and apply the audio signal to only one tube. The unused tube will provide DC balancing the first tube, just like in a standard PP.

[ER]

It can be done on the ends but don't use the center tap. Also like other have mentioned you'll saturate the core more easily, so you need to use a much bigger tranny to get away with it, a 10W tranny with 20K primary is useless for this. That sounds pretty high, more like an interstage transformer.

I really like the open frame 10 and 15 watt edcor trannies for single ended and they're only around $20.