[R-390] R-390A 2nd Oscillator alignment...?

[Larry H]

Hi Jordan,  None of the tech refs do this subject justice, especially the
1956 Army version (it's totally missing).  This is very noticeable because
of the frequent discussion on our forum.

Although I haven't tried it, I like the R-390/URR tech refs process, but it
too does not discuss the very common situation where some components like
the crystals and SM caps may have drifted value and this requires a little
more finesse.  What you will most likely end up with today is some of the
trimmers are at or close to the end of adjustment, some in one direction
and others in the other.  When the situation is at hand where a trimmer is
at end of adjustment, the T401 needs to be adjusted slightly so that all
the trimmers can be adjusted where they are not at the end of travel.  If
this is not possible, then replacement of a crystal that has drifted too
far off frequency needs to be replaced or the trimmer or its parallel SM
cap needs to be repaired or replaced.

As far as instability goes, I've only seen that when the trimmer involved
needs to be cleaned or an SM cap is going bad or some connection is bad.

Regards, Larry

On Fri, Nov 19, 2021 at 1:12 PM Jordan Arndt <Outposter30 at shaw.ca> wrote:

> Hi again group...
>
> I'm wondering if there has been a consensus as to a reliable way to set
> T401
> in order to perform the alignment of the 2nd Osc. and the variable
> capacitor
> bank...?
>
> I've read and tried a number of various methods published by users and
> what
> can be found in the various manuals including the R-390 non-A manual,
> which
> is the procedure I have finally resorted to in order that the oscillations
> in this '60 S-W deck remain stable, which thus far appears to have worked.
>
> Thoughts, opinions etc. much appreciated....73..Jordan VE6ZT
>
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