[LarryFS]

I recently refurbished a 1935 Philco 620B with new electrolytic caps, new tubular caps, and new resistors for those that were out of tolerance.  The radio plays well but has a quirk in its power up.  When I first turn it on, there is the expected delay as tubes warm up.  After about 13 seconds I'll hear low volume audio.  About 8 seconds later there is a click and the low volume audio instantly becomes normal in volume.  The radio continues to play normally thereafter.  Where do I start in trying to eliminate this quirk?  Is it likely a tube issue?  I've tried swapping the output 42 tube with another and still had the quirk.