With my last Lundahl shipment I received samples of a new interstage transformer, the LL2746. This is a 1+1:2+2 interstage transformer on a larger core for high current driver tubes.
The datasheet gives 45Hy primary inductance for the version gapped for 30mA. As most Lundahl transformers this one also can be ordered with different air gaps for various currents. The 30mA version seems just perfect for a 45 drives 45 power amp. With primaries as well as secondaries wired in series it will provide a 1:2 step up ratio which is very helpful since the 45 has very little gain as driver tube. This gives a 6dB boost. Of course the transformer could also be wired as 1:1 when primaries are configured in series and the secondaries in parallel. With the air gap sized for 20-25mA it would also be usable with a triode connected 46.
This interstage transformer is quite big. It comes on a larger core which is also used for small output transformers. Here a size comparison between the LL2746 and the LL1660:
I haven't tried these transformers yet. They will certainly find their way into a future 45/45 amp!