I Remove the transformer to take measurements.

here are my results:

The inputs seems Ok to me, there is only the Red Output (675 Ohms) which seems to be wrong.

But the wiring diagram that I deduce from my system is different than the Sonavor One  :"/forum/beogram/beogram-400x-projects#post-2220819;

Correct.  My drawing was for the voltage switch at the 130 VAC setting which is what I am using.  Yours is for the 220 VAC setting.

Yes but it should be the same transformer for every voltages

I was meaning that I the 5 inputs of my transformer are not connected the same way as yours.

Your schematic has more sense to me in the way that you keep one 2 inputs Red/White (upper) separate coil and a 3 inputs coil (Lower) Yellow/Green / Black.

My schematic is using a B&O schematic on which I simply apply the cabling color effectivly present on my BG4000.

Right, your diagram is what the Beogram 4000 service manual schematic shows in the circuit.  That is the 220 VAC selection.  The voltage switch changes the connections between 1, 2, 3, 4, 7, 8, 9 and 10.  I re-drew the service manual schematic with the 130 VAC connections to figure out what I should be seeing. As it turned out my transformer was bad so I had a toroid replacement made. Because I am located where line voltage is 125 VAC I didn't replace the top secondary which needs to be 220 VAC (50Hz or 60Hz) for the strobe lamp.  125 VAC, 60Hz won't drive the lamp.  I ended up making a strobe out of a rectifier and LEDs.  So no more voltage switching for my Beogram 4000. 

For a new transformer 

   - how many Ampere is necessary for the 24VAC output ?

   - How many Ampere is necessary for the  6 VAC output ?

As the main power is 220V , can I connect the strobe directly on the line voltage with a fuse in between ? (what should be the amper value of the fuse ?)

I used 1.5A RMS on the 24 VRMS secondary and 0.4A RMS on the 10VRMS secondary.

I wouldn't run the 220V primary to the strobe circuit.  Are you going to try and have the new transformer support primary voltages of different values (via the voltage selection switch) like the original?  Or are you going to make the transformer for 220V only?  If the latter then just include a 1:1 secondary for the strobe.

I will probably go for a 220 V only transformer.

I would prefer to have a toroidal model in order to have a better audio signal without any Hum, but it will be probably diifcult to find a small one that will fit in the space, with the 3 outputs

Why is it better to get the strobe signal from a secondary 1/1 instaed of the primary ?

If you pull the strobe off the primary then you are essentially plugging the strobe directly into the wall outlet. That signal would pass through the little power supply board for the switch. It would work but I would feel better with the isolation of a secondary like the original had. I didn't find any ready made toroid transformers for my Beogram 4000 so I had a transformer company here in the USA (Toroid Corporation -