75a_4 alignment questions

[W6MQI]

Been doing a full alignment on a 75a-4 receiver all has gone good so far radio seems to play real well.
But two things remain 80m Tweet trap adjustment, and AVC threshold adjustment.

The tweet adjustment won't null the 3.533 birdie at all L23 can be adjusted from end to the other with only very-very minimal nulling of the birdie. I tried a few things like making sure all grounds in near by circuits are solid, even tried different value capacitor for C-140 just for the hell of it nothing seemed to affect the nulling.

With regards to the  AVC threshold R-9 adjustment I'm not sure what the manual is trying to tell me what to do? If someone could put this in plain English so a neophyte can understand much appreciated.

Dave 

[W6MQI]

So I did some more test with the tweet adjustment and noticed that if the antenna was hooked up to the receiver I was able to null out the birdie, remove the antenna no null. Not too sure what that's about  but I'll take what I can get. Only outstanding problem now is the AVC threshold adjustment.


Dave