I have seen a bizzare set-up in an old Bell radio-gram here that had a single (E-I) laminated steel core and the audio windings were on one side of it and on the other side was a single winding that acted as a choke for the power supply section, for smoothing purposes.
It's a cost saving scheme I've seen in some low cost foreign radios, where half wave rectification is used with low value electrolytic filter capacitors.(i.e. lots of 50c/s hum on the B+). The filter choke winding on the output transformer is connected out of phase with the normal high impedance winding fed from the output valve. Effectively the ripple present on the B+ supply is cancelled out. It's still there but you no longer hear it.
