Been doing a little more troubleshooting on the 1320 looking for the source
of drift after a couple minutes of transmittingâ?¦ I removed the cover and let
the radio stabilize for several hours. After heating the tip of a
nonconductive probe with a hairdryer, I touched various components in the VFO
circuit, and found that oscillator Q2 (2N4124) is VERY sensitive to heat.
Holding the probe to the side of the transistor will cause immediate downward
drift.
Varactor D1 (MV209) will also cause downward drift, but is slow to react to
the temperature change. (Inserting the probe near some components without
heating it does cause some change in frequency, but no drift. I took that
into consideration when performing these heat tests.)
Touching various capacitors in the circuit causes some upward drift, but the
reaction time, to me, doesn't even approach Q2's. Personally, I don't see
any way the capacitors can react quickly enough to offset any negative freq
drift caused by Q2.
Note: I turned the fan on when I sat down to write this e-mail, and listened
to the VFO freq change. It stabilized after moving 165 Hz.
Questionâ?¦ Is it normal for a transistor to be this sensitive to heat?
Thanks for helpâ?¦and patience. (Solder connections in the VFO, buffer and amp
stages have been re-soldered.)
73,
Joe ( WJ5MH )
Wj5mh@aol.com
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