[Arran]

 Given that this is an early 1940s model with loctal tubes dirty contacts in the tube sockets can be a problem, as well as oxidation on the tube pins themselves. You may also have a problem with a cold solder joint or even one that you forgot to solder. The Candohms are worth checking as well. As far as I know Philcos of this era did not have many problems with the mica caps, except the ones that are wax dipped and used on some pushbutton banks,  I think that the IF cans mostly used trimmers rather then permeable slugs for adjustment, even so they would have used molded micas inside anyhow.
Regards
Arran