[Hallicrafters] S-38 BFO and hum problem

[Craig Roberts]

Merry Christmas fellow 'crafters!

I've successfully restored several S-38-series receivers (fun n' easy projects, eh?) and am presently finishing up a former basket case "original" S-38. It now plays well with the usual and surprisingly excellent sensitivity and selectivity, but has two aberrations that have never shown up in any of my later S-38 models. though: 

1) There's a low-level ambient hum that's not affected by the volume control. I've replaced the electrolytics, of course, and checked all solder joints, ground points, etc. I'm thinking it may be because the S-38's circuit uses smaller value filter caps (40/30/30/20) than the later 60/40/40/20 types. Could that be? 

2) The BFO injection is insufficient. I've played with the "gimmick" capacitor and installed a new 12SQ7 and related components (except the mica caps) and there's still no oscillation to speak of (certainly not enough to copy CW or SSB). I know I'm missing something obvious, but what could it be?

Any suggestions would be most welcome.

Many thanks, 73 and Happy Holidays!

Craig
W3CRR