[R-390] How To Adjust the Calibrator on a non-A

[Tom Norris]

Harold and the group

What is happening is that the crystal in your crystal
calibrator is off freq. Find the calibrator chassis -
It's on the bottom next to the PTO - it will have a
crystal oven and 2 12AU7's on it (V901 and V902).
Between the crystal oven and V901 there is a trimmer
cap with a metal shaft. This is trimmer C901 ( don't
touch the small ceramic trimmer cap between the tubes.)
With an antenna connected, tune to WWV and adjust
the BFO to zero with WWV. Then put receiver in CAL
mode, (make sure you have not touched the BFO knob
in the mean time) zero beat the cal signal by adjusting
C-901. Double check afterwards by making sure the
cal marker is now every 100 kc. If not, skip a
paragraph and read what to do in the unlikely
event that it's still screwy.

Alternately can adjust the crystal for exactly 1.0000 MC
using a frequency counter. Best way to couple your counter is
to take the shield off V901 and wrap a few turns of wire
around the tube for a pickoff. ( Usually works for me)
With the second method it is easier to see if the
other non-touchable cap needs adjusting. If don't
have a counter, the WWV method is what is outlined
in the manual, and should be considered good enough.

If the crystal will zero beat with no problem, and the
points are still off, you will need to go to the cap I
said earlier not to touch. Best way is to use a freq
counter then adjust the ceramic trimmer C912 for
exactly 100 kHz out. (several turns of wire around
V902 will maybe give you enough to see the signal. ) Most
likely you won't need to adjust this trimmer if all else is
normal. The 1 MC cal crystal does age over time and it is
normal that it will need to be adjusted now and again as part
of your regular PM.*

It's really not as hard as it sounds, I just tend to
ramble when I try to explain procedures.


Tom NU4G

*You do do regular Preventive Maintenance on your radio,
check and lube the gears and racks, burnt wiring, mouse
nests and rogue ukkumpucky? Shame on your if you don't. ;-)


>Hi All
>
>I have a Motorola R-390(non-A). The calibrator makes a tone 
>approximately every 90 Khz., not every 100 Khz.. For example: 14000, 
>14090, 14180,14270, 14360. Do any of you have any words of wisdom 
>for me? Thank you in advance for any help.
>
>Harold Alexander
>Modesto, CA
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