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Replacing centre-tap transformer with standard transformer

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Hewitson:
Hi guys,

I have here a cheap chinese set of 5.1 PC speakers I'm trying to repair for someone in which the transformer (14.5V centre tap) has gone open circuit. It is quite a large transformer and I am unable to get anything like it locally, and ordering from overseas would likely cost more than the unit is worth.

What would be the best way to replace this with a standard transformer?

Cheers

alm:
Assuming the secondary windings are in series, you can replace it with two transformers (primaries in parallel, secondaries in series, watch phase) with about half of the total output voltage and power each. If they're in parallel (unlikely), you can replace it with a single winding.

Simon:
is it actually using the transformer to produce a dual supply ? A long shot I know but I've often seen dual secondary transformers used for a single supply and only use 2 rectifier diodes, but this is characteristic of small supplies, if your dealing with a proper power amp it probably has a proper dual supply.

Another option is get a single output transformer of twice the amperage and use a voltage doubler rectifier to double the voltage an have a common reference, you will need to replace the rectifier and smoothing circuitry as well

Zero999:
Is that 14.5-0-14.5V or 7.25-0-7.25V?

If it's 14.5V just use a 15V transformer, if it's 7.5V you might be all right with 6V but it may need to be 8V

JohnS_AZ:
This is a total guess, but I'd bet it's a bipolar power supply. Probably something like a 30V center-tapped transformer and a power supply circuit to provide +12V/Gnd/-12V. That's really common in higher power audio amps. The TDA2050 amp I'm building is set up for +22V/Gnd/-22V.

If that's the case, two 15V transformers would work; primaries in parallel, secondaries in series with the center point being ground.

I've read dozens of times that you have to keep the primaries in phase, but I have never figured out why, or how to actually tell. Since you're ultimately making DC, what's the difference??

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