[R-390] Frequency Shift With AGC Level

David Wise [email protected]
Mon, 21 Apr 2003 10:30:01 -0700


> From: Jim Miller [mailto:[email protected]]
>=20
> I've noticed that with the BFO on a strong carrier, when I=20
> lower and raise
> the RF Gain, there is a slight change in beat note pitch,=20
> maybe 100 cycles
> or so.  This doesn't happen on my other 390a.  Have swapped=20

Since the oscillators are unbuffered and not all of the B+
is regulated, there is a certain small unavoidable shift.
However, there is also possibility of avoidable shift.
Make sure the 0A2 is regulating.  One of their wearout
modes is a rise in breakdown voltage.  Combined with
high screen current and low line voltage, it may be
dropping out.  Note also that the BFO uses unregulated
B+ .  If you can rig up a stable external BFO, it will
help isolate the shift.

73,
Dave Wise