Power transformer

[martin manning]

Basically that’s it, but the phasing of the two primary windings is critical, so you will have to make some measurements to sort that out, and also to identify the wire that will be exchanged for the 230V configuration. You said you are on 230, not 240, right?

Question: Do the black and black/white wires on the fuse holder tail, and the white and white/brown wires on the IEC inlet go directly into the transformer?

[salvady68]

Yes, the wires go directly to the trasformer, the black goes to the opposite side of the others. Yes I've said 230 but a few years ago was 220V, now the standard for italy is 230V with 10% tollerance I just measured with the voltmeter and gave me 228v, so I confirm 230 and so it is not enough to put in series the two windings but as you say, we must also find the additional winding for the 230V

[martin manning]

Ok great. So lets assume that what you have now is as shown in the diagram below. Do you still have the step-down transformer? If so, power it up and measure the AC voltage from the fuse holder (black and black/white) to the gray, to the brown, and to the white and white/brown on the IEC inlet (that last one should be the step-down transformer output voltage, about 120V). Post those measurements.

[salvady68]

here I am! from black and black/withe to gray 99V
From black and black/white to brown 90V
From black and black/white to brown/white 90V
From black and black/white and white/brown 108V

[martin manning]

here I am! from black and black/withe to gray 99V
From black and black/white to brown 90V
From black and black/white to brown/white 90V
From black and black/white and white/brown 108V

Do you have three unconnected leads, gray, brown, and brown/white (meaning a brown wire with a white stripe)?
And, in the last line above do you mean black and black/white to the IEC inlet, white and white/brown?

[salvady68]

Yes, I have three unconnected leads with thoose colors, yes sorry I have 108V to the IEC inlet

[martin manning]

Ok, great. Correcting for the low (108V) output from your step-down, it's looking like the diagram below.

Now you need to desolder the transformer leads from the fuse holder and the IEC inlet, separate them, and determine which colors go to which winding:

Measure ohms from black to all of the other leads (all six of them).

Some will be very low resistance, and some will be infinite. Or, if your meter has a continuity function you can use that. The ones with continuity or low ohms to black are on the same winding as the black, and the ones with no continuity or infinite resistance are on the other one. Post the results.

[salvady68]

Cool! Unfortunately now I’m at work and I can’t go home until tomorrow afternoon...
I can’t wait!

[salvady68]

Ok, let's go

Black ----> white 2 Ohm
Black----> brown 1,6 Ohm

Black/White ----> white/brown 2,1 Ohm
Black/White----> gray 2 Ohm
Black/White----> brown/white 1,7 Ohm

[martin manning]

So the upper winding is black, Brown, and white, top to bottom in my drawing. Lower winding is Black/White, Brown/White, Gray, and White/Brown.

I believe you want to take the black to the fuse holder tail, join Black/White and White, and take gray to the IEC inlet N. 120+110 to get 230. Make sense?

It would be good to put a small AC voltage on first and check that the voltage from Black to the joined wires is about half of Black to Gray.

I’m out and about right now, so phone only.

[salvady68]

Ok! First i have tried with the stepdown transformer...seemed all ok. Now I have tried directly with 230V and I have 480V on anodes, is it correct? With stepdown transformer was 420...but I have only 108V instead 120V

[martin manning]

Seems reasonable... 120/108*420 = 467. The biggest danger is getting the phase wrong, which you obviously haven’t done. Check your line voltage and see how close it is to 230. If it often runs high, you could wire for 240V, by taking White/Brown to the IEC N, and bring the anode voltage down a bit. Below is what you have now, I believe. As a check, Black to White/Brown should now measure about 10V higher than your line voltage. Don’t forget to reduce the amp rating of the mains fuse by half. Good work!

[salvady68]

Thanks for the diagram! I will print, and keep it! I had measured the voltage on capacitors, when the amp was in standby, when is on, the tension is 468V, and the power trasformer seems less hot then I was use step down transformer. So I think 230V is the better choice, also because the line is 228V
Thankyou for all, God bless you!

[martin manning]

All good then! You're welcome, it was a fun little puzzle to solve.

[salvady68]

it was a fun little puzzle to solve

The guys at magnetic components replied me!
Martin you had perfectly guessed!