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mastero 13th October 2006 08:44 PM

Need help to understand a salvaged Transformer.
Hi all,

I have salvaged this transformer from a panasonic Hi FI
this thing weighs like 5 kilos.

It looks like a nice transformer to just throw it..

Above are the pictures of the transformer... what i have figured out till now is it has

Three secondary output. The first two is X - 0 - X and the third one is X-0

Now How to findout the value of X..?

The primary has five wire but only two are connected to the mains, while testing it with a line tester (the one with led ) it glows on all the pins touching any pin to any pin showing they are connectd internally.

Any help is good


rehanabid 14th October 2006 08:17 AM

This is a transformer which is designed around mutilple primary voltages which are normally like 110 VAC, 117VAC, 200 VAC, 220 VAC and of course one wire would be common, you can use those two which show highest resistance value when checked by a digital multimeter, that would be the two extreme ends.
for the output or secondaries there is no way you could get a reading without connecting it to mains, a wild guess would be 18-0-18, and 0-12 V.

AndrewT 14th October 2006 08:31 AM

buy a digital multimeter (DMM) with DC and AC and resistance ranges on it.
Try to get one that has 200mVac to 600Vac on the range selector.

Build up a mains light bulb protection unit.
It will help stop you blowing fuses, but more importantly it will prevent you blowing up the transformer or your next project if you mis-wire something.

mastero 14th October 2006 09:06 AM

Andrew i have a DMM and when i checked it for voltage i got

38-0-38 (Heavy gauge wire is used say 19) and 16-0-16 and 0-7

Abidr u were close :) my guess was also the same primary is for mulitiple input voltage shall not touch it as i only want 220V

So if i rectify the 38-0-38 what shall be my DC output ? as this is a heavy gauge wire so i assume more amps.

Similary for 16-0-16 and 0-7

I am planning to use this for my 5.1 system

3 X 4780
1 X 3875



AndrewT 14th October 2006 10:11 AM

Re: Need help to understand a salvaged Transformer.

Originally posted by mastero
Three secondary output. The first two is X - 0 - X and the third one is X-0

Now How to findout the value of X..?


for voltage i got 38-0-38 (Heavy gauge wire is used say 19) and 16-0-16 and 0-7
You seem to already have the open circuit voltage.
That will give you the DC voltage after you multiply by square root of 2.
Subtract the bridge voltage drop (about 0.7V per half bridge).

so 38-0-38Vac >> 53.7 -0.7 = +-53Vdc.

Same for the others.

As you load them the AC voltage will drop towards the rated voltage but you do not have access to those numbers.

What is 19 gauge in mm diameter? not sqmm.

I do not have the datasheets for your chipamps, but 38Vac is way over what a chipamp can handle when driving most speaker loads. This transformer may have been designed for use on a 100W into 8ohm discrete amplifier.

mastero 14th October 2006 11:28 AM

19 SWG is around 1 mm

I am going to wire it up and findout exactly what the numbers are shall have a light bulb as load :)

Ciya soon if me not fried ;)


AndrewT 14th October 2006 12:00 PM

1mm wire is good for about 2.4Arms from the secondary.

This equates to a continuous 1.2A at +-53Vdc after the smoothing caps. It confirms the 100W guesstimate for maximum output power.

I will further guess the original manufacturer ran two channels off this pair of secondaries. i.e. 100W + 100W into 8ohms and relied on music duty to prevent overheating of the transformer.
An alternative use would be 200W into 4ohm for music duty or for good bass and little droop in supply voltage an excellent 4 to 8 ohm or 6ohm power amp.

mastero 14th October 2006 02:04 PM

The speakers out put says 4ohms...

Has two pairs of speaker connection only.

I checked the 4780 and 3785 data sheet its maximum (V-) + (V+) = 84v so there is no chance i can use this transformers first winding forthis purpose. :( or can i ?

Now i have the second option the 16 - 0 - 16 what will the DC volts be for this ? (I am a bit slow with calculation :()


AndrewT 14th October 2006 02:21 PM

go a read the datasheet again.
The 84Vdc is absolute maximum voltage. NOT operating voltage when driving speakers. This is equivalent to +-42Vdc on dual polarity PSU.

Going above 84Vdc is likely to cause permanent damage to the chip amp, if not immediately then in the longer term.

Have another read of the datasheet.
What is the maximum voltage when driving 8ohm speakers?
What is the maximum voltage when driving 4ohm speakers?
Are these different?

Do you have any 4ohm or 6ohm or 4 to 8ohm speakers?

Then choose a supply voltage to suit the low impedance speakers.
If you connect low impedance speakers and drive them hard when the supply voltage has been selected to suit high impedance speakers, then the best that will happen is that the chipamp will current limit (not very nice to music), or go into thermal shutdown to prevent permanent damage (again not very good for music).

You really do need to read that datasheet.

What is the wire diameter on the 16-0-16 secondary? It is unlikely to be the same thickness as the 38Vac winding.
It is more likely this went to some voltage regulators to supply the pre-amp section of the amplifier. This duty could be just a few tens of mA upto a hundred or so mA.

mastero 15th October 2006 08:33 AM

Yeah ur right it wont help as it is ...

Time to rewind the transformer ... for trpple secondary winding :)

mostly gonna make it 16 - 0 - 16 x 3 nos so i get +/- 24vdc after rectifier


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