[Arran]

Bob;
I was just thinking that maybe the 1R5 tube doesn't like being operated at 1.2 volts on the filament, though you did mention running the set from batteries with the same result. From what I remember 1R5 tubes can be quite particular about voltages on the plate and filament, 1/10th of a volt too low and they won't oscillate, though the set is getting reception so it must be oscillating. Have you compared the service info between the Motorola and the Roger-Majestic, and the Phillips versions? I'm kind of wondering why the Phillips used a 150 ohm resistor verses a 160 ohm in the Motorola after the selenium rectifier? Was there a problem with the larger value?
One more thing to check, what about the loop antenna in the lid, is there good continuity? Are the leads connecting it good with good solder joints? It sounds too obvious but I've noticed AC/DC radios play poorly with one end of the loop antenna open, weak reception, with garbled audio sometimes. This thread makes me want to get into the set I have, though I probably should not.
Regards
Arran