[HomeBrew] Transformer

[La6wea]

Can anyone tell me how to calculate the turns of a transformer. I have =
rewinded several transformers but then I have been able to count the the =
turn pr volt of the old windings, but now I have only the iron so I =
starting from the bottom.
The cross  area of the core are 2 1/4 by 3 1/2 inch and the length of =
the bobbin are 3 inches.=20
I want to wind a transformer with 230v primary and
a 1200v Hv winding with as much current I can get.
The weight of the iron are app. 20 pound.

Tnx in advance Ken