[Radioroslyn]

Oh my It use to be a 38...

Plan B. Use the diagram from the model 60 to check the wiring and signal path of this set. Pretend (look up the tube's basing info to see what needs to go where) that the 42 is a 41. If you try a 42 in this set there a good chance that you could damage the opt from too much current flow. Since you have a 6A8 I wound check the mixer socket wiring and see what it's wired for. Use the 6A7 circuit from the 60 as a guide to sort the mixer. 6A7 and 6A8 are electrically the same but one uses a standard base and the other a self centering base. The power supply is going to be a little different as the 38 uses a pm spkr which has no fc. So there's probably going to be a resistor between the two larger value filter caps. Not sure how the bias is developed for the 41. It may have a resistor from pin 5 the the chassis (cathode bias). Or in Philco style there would be a resistor in the center tap of the hv winding to the chassis like the 60 (fixed bias).

Have fun chasing electrons!