I work for a charity which sends donated school science apparatus to schools in developing countries. We carry out basic repair work where possible. I am looking for a transformer to convert between 3 and 24 volts. RS item 504773 has the correct turns ratio and is the correct size but it doesn't work in my application because the coil resistances are too large. The coil resistances needed (measured as d.c. rather than a.c. impedance) are about 0.7 and 14 ohms. Is such a transformer still made or was it a special for this apparatus which is no longer made ?