[R-390] zero adjust knob

[jm]

Hi fellows

I have an annoying problem with the zero adjust knob. When I use the
calibrator of the receiver things are well.

The problem arises when I try to zero-beat using a broadcast station with a
known frequency.

Loose the knob, zero-beat and when I am tightening the knob I can realise
how the signal measured with the carrier meter begins to decline. The more
I tight the more the needle descends. The final result is a mismatch of 1-2
kcs.

It is strange for me that the problem occurs only in the AGC o MGC position
and not with the calibrator.
Can you help?

Thanks and regards

Jose Isasa
EA8DCP