It might need to be wired in series with the rectifier output, if wiring it between the smoothers then the field coil will only be passing the current flowing through the mixer, IF, 1st AF stages which might not be enough to give a decent flux density.
You could also connect it from the HT to line neutral via a suitable dropper, if the rectifier is up to it, not sure what the HT current consumption is in a typical 4 valve (excluding rectifier) radio is maybe 40 ma..ish? (in relation to your 300 ohm coil which was probably series fed) If so then use that as a basis for working out a ballpark dropper resistor value.
Lawrence. EDIT: Didn't write the original very clear, have now made a few amendments to what I wrote originally.
You could also connect it from the HT to line neutral via a suitable dropper, if the rectifier is up to it, not sure what the HT current consumption is in a typical 4 valve (excluding rectifier) radio is maybe 40 ma..ish? (in relation to your 300 ohm coil which was probably series fed) If so then use that as a basis for working out a ballpark dropper resistor value.
Lawrence. EDIT: Didn't write the original very clear, have now made a few amendments to what I wrote originally.
