PT 240v to 120v tap wiring

[shaun]

Heyo,
I'd be surprised if this hadn't been covered somewhere here before, but it isn't appearing when I search, so maybe someone can point me where to look. In any case, this is pretty straight ahead.

I have a PT with two 120v primary taps, as per the first diagram attached - that is the actual schematic for the PT. It is currently wired with both taps in series for 240v VAC input (it was imported from Merry olde England).

I want convert it 120v VAC input, so I know I'd use only one primary tap. But I came across the second diagram, which indicates running the two primary taps in parallel for 120v. I was hoping someone here could enlighten me as to why this is necessary: i.e. why not simply tape off one of the taps? There must be some kind of current running through the 2nd primary tap even when only one primary tap is connected, so I guess the parallel design deals with that somehow. I'm hoping to understand what running the 2 taps in parallel achieves. Clearly, there would be the resistance of the two windings to consider.

Thanks, and hope you're having a great day.

[PRR]

You want to use ALL the copper you paid for. If you are running half the voltage, for the same power, you must be running twice the current. So you need copper of twice the area. Or two strands of the original area.

You don't say what this is. A Germanium fuzz or an arc-welder. Small transformers you can get away with a little cheating. They have enough surface for their volume that they can hardly overheat too much. (But knowing that, the winder may have used the very cheapest varnish.....)

I would not call those "taps". A tap comes out partway along a winding, like a side-street. This is two windings which can be connected Series or Parallel.

[shaun]

Aha! Thank you PRR. Makes perfect sense.
And yes, two windings rather than taps.
Much appreciated.

The PT is in a HiFi amplifier AQ2002 model, running a 5AR4 rec tube and a single 6V6, plus pre tubes.