Dual voltage transformer wiring help.....

[Paultergeist]

Hi all,

I hope this is going to be easy.....

I am working on a Jurassic-era amplifier which uses a dual voltage transformer primary-side. The idea was that one could plug it in to either 110V or 220V AC power. Once I am done re-working this thing, it will never need to able to be plugged in to 220V, and there is quite a bit of extra wiring associated with this feature -- my plan is to make the amp run on 110V AC exclusively.

The primary side of the PT appear to have (2) identical windings -- each winding having a "110" end and a "0" end. Based on my understanding of how such a PT would be wired:

IF I WERE KEEPING the "220 V" feature, the two primary windings would be in series.

SINCE I AM ONLY going to have this thing run 110 V, I believe the (2) primary windings are wired in parallel. To be more specific, I plan to have both of the "0" winding ends tied together and connected to the neutral in-coming AC feed. The (2) "110" winding ends will be tied together, and fed the in-coming AC "hot" right after the main power ON switch.

Does it sound like I have this right?

Thanks for any help.

[martin manning]

You have it right, but it makes no difference which end goes to the hot side of the mains.

[Phil_S]

There is a good reason for parallel wiring of the primaries. Doing that doubles the VA rating of the transformer. Leaving one primary winding unused is a waste of capacity that you may actually need.

0 and 110 are arbitrary designations that are useful in knowing whether the windings are wires in phase. The electrons have no idea if they are moving left to right or right to left. What matters is that the windings are in phase when you hook them together or they will buck each other, reducing power capacity to zero. Either end can be hot or neutral.

You have it right.

[Paultergeist]

Martin, Phil,

Thank you.

I normally would not re-wire an original design to this extent, but there are simply a number of questionable aspects to this amp's power supply (based on today's standards): no AC supply ground, "death cap" on ground switch, in-coming AC running across chassis twice (between front panel and back panel) before it ever hits the fuse --- etc --- I decided to just re-wire this thing for a clean and *proper* and simple power supply.

I believe I am now clear on how to proceed with the PT thanks to your help.

I very much appreciate it.

Paul

[billc]

sound right, Triad sells modern VPS230 series xfmrs that work that way, though it does matter how it is wired to get the phase right as was said....i.e. 2 and 5 are connected for 230V operation, 1 to 5 and 2 to 6 for 115V. The digram below might help with rewiring....

[img::]http://media.digikey.com/pdf/Catalog%20 ... _schem.jpg[/img]

[Paultergeist]

That is a helpful diagram, Bill.

Thank you!