Trévoux Transformers

[roberto]

Hi,

I've recently bought a small hi-fi output transformer on a street market at something around 10 euros.
It's a push pull UL OT made in Paris by the company TREVOUX (probably Trévoux, but it's written in capital letters).

It's a small EI transformer inserted in a metal box (to prevent electromagnetic interactions I guess) with the following indications:

Code: Select all

A1 S1 C S2 A2

1  3  5  7
2  4  6  8

  200/15

so the first line it's quite clear. Second and third I guess are four secondaries.
They are connected:
1 alone
2 with 3 and 5
4 with 6 and 7
8 alone

200/15 could be the impedance ratio, but seems too low, and also not clear with which configuration of the secondary.

Does anyone knows this French brand?

I will be able to post some photos only the next weekend, when I'll be back home.

Thank you in advance
Roberto

[pompeiisneaks]

I don't know the brand, but it could also be two voltages. 200 and 15 for the two windings that seemed to be marked.

A1, A2 and S1, S2 with C as a center tap?

My google fu is turning up nothing on the transformers, seems there are plenty of jobs in Trévoux though

I used to live in Lyon but never got up to Trévoux.

~Phil

[roberto]

Phil, donc tu parles français!

Thank you for your research, nothing found also from my side.

Yes, it's Anode1 Screen1 Centraltap Screen2 Anode2
The dc resistance confirms it.

What do you mean by voltages? Windings ratio?

[pompeiisneaks]

Mais bien sur!

Actually now that you said the naming of anode and screen, I take that back, I wasn't thinkign OT, I was thinking PT.

I think then that you're possibly right, because 200/15 is 13.3333333/1 which is an odd one to write that way

~Phil

[tubeswell]

Hook each end of the primary winding to a VAC source (say about ~100VAC end to end, or 50VAC primary to CT) and measure the VAC between each set of secondary taps.

100:2.2VAC = 2000:1R
100:3.1VAC = 1000:1R
100:4.5VAC = 500:1R

[Phil_S]

What Tubeswell says. First test for DCR to see if any are connected internally. You might get a few hints along the way, but often the secondary on an OT shows very low DCR. Then check all possible combinations for output voltage. Eventually, you'll determine what the various output ratios are and from there the impedance ratio. I've done this. It isn't nearly as challenging as it first seems. You can be done in less than 15 minutes. I like to run wires to terminal blocks and take the measurements at the blocks. Needless to say, screw down the blocks. The 5 minutes you spend stabilizing all of it will speed the test and help a great deal with safety. Good luck.

[roberto]

Thanks guys. I usually apply 6,3V on the secondary, but in fact for this kind of OT it's better to apply a known high voltage on the primary, so there's no risk to pass the maximum voltage for the insulation.

Is there any risk that the wax that covers the trafo becomes hygroscopic with the age?

Thanks again in advance.

[roberto]

Is there any french guy that can have seen/used this brand in the past?
Just to know how it was rated.

[ChopSauce]

Maybe you can ask there : http://www.projetg5.com/phpbb3/index.php ?

[roberto]

Thank you ChopSauce, I will try!

As for the transformer, I've done the tests yesterday.
I've found this PT unused from an old project: http://www.inmadout.com/download/pdf/TA34FM.pdf and I've supplied the 180-0-180 V with the 220 Vrms, in order to obtain 129 Vrms from the 230 V tap.

The four secondaries give each 1,47 Vrms, so the winding ratio is 87,76:1 and the impedance ratio is 7700:1.
So all in parallel and the ratio will be 7700:1, two series of two parallels and the ratio will be 1925:1, two in parallel, then in series with the other two in series and the ratio will be 860:1, all in series and the ratio will be 481:1.
So it's a 15W PP UL for a pair of EL84s.

I guess the power because of the dimensions and because of the possible impedance ratios available.
Is there any way to know it for sure?

By the way that PT could be the right choice for this OT (it could supply two of them, indeed).
One option is to get around 250V and run the EL84s safely this way, the other choice is to run it at twice the voltage, then add a VVR to be able to limit and further reduce the B+.

What do you think?