Thank you Poliss, but I want to use transformer(s) and 'Passing Contact' switches that I already have for my 00 layout. The basic idea is to obtain a double source of DC curent, one side of the circuit being common to the point motors from one terminal of the transformer, the other having swiched polarity from the two 'polarity reversed' diode rectifiers connected to the other terminal of the transformer. In this way the circuits would be intermittent unsmoothed DC. at 25 cycles per sec but at opposite polarity at the passing contact switch, which feature is the essential requirement.
My post was to find out if anyone had tried this system or had a good CHEAP alternative method. (I've got to sell my 00 gear before I can splash out on 'n')