[Arran]

Actually if these sets are the same as a model 18 other then for the addition of a #37 as a detector tube, the power output stage is not class A it's a class A-B power output stage with three triode connected type #42 tubes. That being said one of the common failure points is a large bleeder resistor connected between the B+ and ground that is mounted across the inside rear apron of the chassis. It's a non standard value, 7500 Ohm I think, so to replace it you have to make it up with a combo of standard value wire wounds.
Regards
Arran