Some basic questions on transformer with two secondaries

[Mooly]

Its easy. You have two secondaries and four wires. With the transformer not connected to the mains identify using an ohmmeter the secondary pairs of wires. That means you pick one wire at random and measure on ohms to the other three. Only one of those three will give a reading. That makes one pair. The other two wires make the other pair.

Now connect one wire from each pair together. That means you have two unconnected floating wires.

Switch the transformer on and measure the AC voltage between those floating wires. If you find you have the expected voltage (twice the voltage of one winding) then the CT connection is correct. If you have a very low voltage or zero then the connections to one winding only must be reversed.

 

[ginetto61]

Its easy. You have two secondaries and four wires. With the transformer not connected to the mains identify using an ohmmeter the secondary pairs of wires. That means you pick one wire at random and measure on ohms to the other three. Only one of those three will give a reading. That makes one pair. The other two wires make the other pair.

Hi and thanks and this is fine. No problem with this.

Now connect one wire from each pair together. That means you have two unconnected floating wires.
Switch the transformer on and measure the AC voltage between those floating wires. If you find you have the expected voltage (twice the voltage of one winding) then the CT connection is correct.
If you have a very low voltage or zero then the connections to one winding only must be reversed.

And i think i have also understood this and i admit ... it took me a while 😱
If i connect the secondaries wrongly, can i damage the transformer ?
This is my last doubt
Thanks a lot again, gino

P.S. by the way the thin primary has been another big disappointment
I do not understand why so thin primary with so thick secondaries ... they are very big in diameters indeed
But if the bottleneck is in the primary ... what is the benefit of such thick secondaries ???
Unfortunately the transformer is immersed in some chalk or similar
Is the white circular thing ... 🙁

 

[Mooly]

You can't damage the transformer doing what I outlined because there is nowhere for any current to flow with the wires still floating.

Wire thickness... depending on the transformer specification (voltage output and current output) its normal to see thicker secondary windings. There is no "bottleneck". A 10 volt 10 amp secondary would have very thick secondary wires and very thin primary wires. It all depends on the transformer ratings.

I'm not so sure its a good idea having a metal clamp over the transformer. You mustn't created a "shorted turn". That can happen on toroidal transformers secured with a centre bolt and where the top of the bolt can touch the top of the metal chassis. I think you're OK at the moment with that because what you have doesn't pass through the centre of the core.

 

[ginetto61]

You can't damage the transformer doing what I outlined because there is nowhere for any current to flow with the wires still floating

Perfect ! this is the main goal in the end ... to avoid possible irreversible damages 😀

Wire thickness... depending on the transformer specification (voltage output and current output) its normal to see thicker secondary windings.

Ok ! Ohm's rule applies. The higher the current the bigger the section.

There is no "bottleneck". A 10 volt 10 amp secondary would have very thick secondary wires and very thin primary wires. It all depends on the transformer ratings.

Let me elaborate a little. I have noticed from Talema datasheet for instance that the size tend to stay the same with the same VA.
I cannot be sure because the trans is potted ... but it could very well be a 500VA thing
This means 2 Amperes flowing in the primary at max power
Ok ... 1 mm of diameter could be ok
By the way i see that also Nuvotem does not provide the sections of the leads

http://www.nuvotem.com/en/products/pdf/0500P1_1001.pdf

I'm not so sure its a good idea having a metal clamp over the transformer. You mustn't created a "shorted turn".
That can happen on toroidal transformers secured with a centre bolt and where the top of the bolt can touch the top of the metal chassis.
I think you're OK at the moment with that because what you have doesn't pass through the centre of the core

The construction of this amp is clearly not that of a masterpiece 😀
It worked just one day ... and it also sounded pretty nice with a nice soundstage
It has also made me change my feeling about multiple output devices
I think the problem was in a relais in the power supply
I tore everything apart 😱
I will test the transformer as a first ... maybe
But the potting ... it is tremendous
Just look here ...
It must be the work of an audiophile 🙄😀
I have a point on potting
Are there any very good sounding unpotted amps ? yes ?
Then why this potting ? it is just stupid
Am i wrong ?
Thanks a lot again, gino

 

[Mooly]

Looks more like a birthday cake gone wrong 😉 It is indeed tremendous potting. I can't say I've ever seen anything quite like that tbh.

The VA rating of a tranny doesn't directly relate to the secondary wire thickness. Suppose its a 1000va tranny with a 2000 volt secondary. That's going to be lots of turns of thinner wire. Yes 🙂

 

[ginetto61]

Looks more like a birthday cake gone wrong 😉
It is indeed tremendous potting.
I can't say I've ever seen anything quite like that tbh.

😀 just image my expression when i opened it ... i was even scared
I do not even understand what they have used because it is slightly rubbery ... like some plastic ??? it is not chalk
For this reason the builder should be an audiophile

The VA rating of a tranny doesn't directly relate to the secondary wire thickness. Suppose its a 1000v tranny with a 2000 volt secondary. That's going to be lots of turns of thinner wire. Yes 🙂

the ps casp are 40V ... so i guess a 24+24 thing ...
That for a 500VA gives around 10A per secondary ... not bad i think
Also the caps are nice white 10,000uF from Rifa
This make me wonder if the real secret for a good sounding amp lies in the quality of its power supply
I will measure it anyway ...
Thanks again, gino

 

[Mooly]

Ok. Just be careful what you are doing.

(I wonder if the transformer was noisy and that is why whoever covered it in that stuff)