@ NRamaswami

I drew the cores in red-to-blue color to indicate the two polarity in same element.
As you say, they change depending of time due to AC.
This way of coloring, is a conventional representation that means two polarity.
It is used commonly when representing the two poles of a magnet. Therefore in the setup drawn, opposite poles are facing.

@NewtonII
I tried a similar one WITHOUT the two secondary beneath the primary, and without AC, but pulsed DC via a double commutator.
I`ll keep on going

Hi Forest:

I said it earlier.. We have used 1300 metres of 4 sq mm wire in building the device. Each core 18 inches long. And so we had electromagnets for about 5 feet for the rods were coming out of the tubes on both the sides. So it is about 5 feet long. I think the rods would have weighed about 150 kg of soft iron. You need bulkier iron core to have a lot of turns. Small iron core does not work. Each core when wound with a single wire has 80 to 90 turns..This is because we have used the same wires again and again and cut them and then connected them again using tapes and at these places the wire is thicker and so we do not get the same number of turns.

Larger the diameter and longer the length better is the output.

I do not know the theory and so I can only tell you how much the voltmeter and ammeter showed. I cannot even guarantee that the devices are perfect for the devices are cheap analog devices.

You can also use pulsed DC but the results are better with AC than with pulsed DC.. But for feedback purposes I think pulsed DC would be easier to implement..

ALVARO_CS:

thank you for the explanation. I did not know that color scheme.

Hi Forest:

I am not able to understand the question on Quadfilar primary..

What we did is as follows..

1. Wind single layer secondary on tube 1 acting as P1. Each turn may have about 85 to 90 turns. Wind three layers of wire. Go down first from top to bottom and then come in the same direction from bottom to top and then go down again from top to bottom always winding in the same direction.

2. Now wind the 4 wires which are in parallel to each other as primary again as above but here the quadfilar coil ends at the top and not at the bottom of the tube.

3. When the winding is completed for four layers or six layers of such quadfilar coil, connect the end of the first wire to the beginning of the second wire and end of second wire to the beginning of the third wire and the end of the third wire to the beginning of the fourth wire.

4. Now wind a similar P2.

5. Now wind the secondary single layer of multiple layers.

6. Place all them. Now connect the end of the P1 fourth wire to the beginning of the P2 wire 1.

7. Connect all three secondaries in series and connect them to load.

8. . Input is given to the beginning of P1 first wire and end of P2 fourth wire.

That completes the set up..Variations to increase the rate of change of magnetic flux are possible but I have not tested them yet..