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jkuetemann 23rd May 2013 04:17 AM

Possible to reconfigure Toroidal Transformer?
I have been given four 250VA toroidal transformers that came out of some active speakers, RCF Art 300A to be precise. I'd like to be able to reuse these but have one issue. The amplifiers in the RCFs were class G, quad rail (high/low +/-) and so the transformers in question are 60-30-0-30-60, dual 115V 50/60Hz primaries. Searching for the code# 81751094 gave me nothing. I have no use for the 60V windings, but the 30V are perfect for my needs.

My question, does anyone know if these are separate 30V windings configured under the insulating wrap in the above configuration? If so would it be reasonable to think I could reconfigure it to be a higher current 30-0-30 transformer by paralleling the appropriate windings?

Any insight appreciated, I'd like to avoid opening one up if there's no hope of getting what I need by doing so.

peranders 23rd May 2013 04:25 AM

How many wires do you have on the secondary side?

jkuetemann 23rd May 2013 04:31 AM


Originally Posted by peranders (
How many wires do you have on the secondary side?

Just five externally, 60-30-0-30-60. Looking to find out if anyone knows a little about its specific construction. The secondaries appear to be all the same wire gauge, but there are two colours of lacquer visible that makes me think there may be two 30-0-30 windings that are in series. If possible I'd like to unwrap (NOT unwind) these to parallel them instead.

AndrewT 23rd May 2013 10:09 AM

The different colours generally indicate that two spools of wire are being used while winding.
It can then be implied that the two colours are bi-fillar wound. This ensures that the number of Turns in the paralleled windings are identical.
You can check this by reversing one winding and get a zero volts readout. If there were a one Turn error, the readout would be the Volts/Turn value, usually between 100mVac and 1.5Vac.

Where the windings are tapped, it is usually possible to separate at the tapping point to end up with two separated windings.
You could end up with a 4 winding secondary, each at ~30Vac.

TonyTecson 23rd May 2013 10:14 AM

it's possible, why don't you post pictures so we can have a closer look?

jkuetemann 23rd May 2013 11:46 AM

2 Attachment(s)

Originally Posted by Tony (
it's possible, why don't you post pictures so we can have a closer look?

Sure thing.

stoN_Cold 23rd May 2013 11:50 AM

This transformer look likes for "H" class amplifier.

Regards zeoN_Rider

jkuetemann 23rd May 2013 12:00 PM


Originally Posted by zeonrider (
This transformer look likes for "H" class amplifier.

Regards zeoN_Rider

You are correct, depending upon regional nomenclature regarding classes H and G. The amplifier module these used to power is what I would refer to as class G (dynamic rail boosting as opposed to hard rail switching). I'm not planning on creating one of the higher classes with these. I'd like to stick with class B/AB and thus the desire to see if I can set these up as 30-0-30 secondaries.

KatieandDad 23rd May 2013 12:01 PM

Measure the resistance between the 60V and 30V wires. I'm expecting the resistance to be lowish indicating that the windings are in series with each other.

stoN_Cold 23rd May 2013 12:06 PM

1 Attachment(s)
Here the PSU schematic.

Regards zeoN_Rider

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