[Arran]

 I don't own a Philco model 18 but own it's successor model a Canadian 3118. For starters do NOT power up the set with the speaker unplugged, unlike most sets leaving the speaker unplugged does not disconnect all the of the chassis from the B+ supply and can overvolt and BBQ some components. As to why the set does not play, replacing the filter caps is only the first step, all of the insides of those black Bakelite blocks need to be replaced as well, and many of the resistors will need replacing as well. Just take it one step at a time.
Regards
Arran