[Drake] R4C receiver sensitivity question

[Martin Sole]

I have recently aquired an R4C that suggests it might be a little
insensitive. Having been through the manual alignment procedure I
stumble at setting the S meter. I can set the zero pot to S3 for 1
microvolt but then the bias R55 does nothing, have tried resetting the
pots to different start positions but always come out the same.
Similarly I cannot get S9+60 for 30mV with the sensitivity pot.

Wonder if anyone has any suggestions?

Martin
HS0ZED