[Mondial]

I would try the physically largest interstage transformer you have with a center tapped secondary. The quiescent plate current of the detector is very low since it is biased near cutoff, so this should not be a problem with any usual interstage transformer. If a problem were to occur, it would happen when the detector is being strongly driven, as when playing the radio loudly. A very strong signal into the detector might cause the plate current to rise to the point where you might saturate the magnetic core, but I doubt you would notice any distortion at normal listening levels.

The usual interstage/driver transformer ( for example 27 audio stage driving PP 45's) should work fine, since this is a more difficult situation compared to the detector driving the transformer directly. With the audio amp driver, the normal primary plate current would be about 5 ma, a level the detector driver would reach only at very high signal input levels