[Arran]

Took a look at the diagram and it looks to be real honey! Has robust power supply and powerful audio output stage. On a lot of the Philco sets that have their triode connected 42's they use an 80 tube for the rectifier which in a ten tube set is pushing pretty close to it's max rating. I guess it's the dollars and cent thinking of the 1930's.

Did see something that is problematic. Across the HV winding of the power transformer there are two paper caps tied back to chassis ground. Those need to get gone! They don't do anything and if or when they short the power transformer goes with them. The National Co (National Radio) after the war did the same thing with caps across the HV secondary. It's pretty common the find these set w/ a replacement power transformer. It's just like having shorted filter caps but it just burns up the power transformer and not the rectifier and field coil.

GL should be a good loud set!

Terry;
   I've noticed that in the early to mid 1930s RCA and G.E didn't mess around when it came to power supply design, on the RCA 143, which only has 8 tubes, but push pull 42s, they used a 5Z3 rectifier. In a Canadian Westinghouse set  I'm looking into, which is electrically similar to an RCA R 78A, they used a type 82 mercury vapor rectifier, and two filter chokes in the power supply, to power the pair of class B connected 46s as well as the other nine tubes.
  But I'm not sure that Philco really did take a chance on the power supply in sets like the 18/118, if the power supply was constructed with a filter choke input that may explain how they got away with using a stand alone type 80. I know that one thing that those Philco with triode connected #42s have is a large bleeder resistor, which is needed with the class A-B power output stage for current regulation, so perhaps this adds a safety factor?
   I don't know why they would add capacitors across the H.V winding, perhaps they were worried about power line transients, but it would be more normal to connect those across the primary, or rely on an electrostatic shield in the transformer itself for that.
Regards
Arran