[R-390] A Few R390A Issues Zero Adjust

[Grant Youngman]

Thanks, Roy ..

It does appear to be related to sync (or not) of the multivibrator.  Even
after adjustment, it will eventually begin wandering in and out of sync, and
rather than a nice cal tone at the correct frequency I get a rough buzz well
away from where it should sit.  That may indicate the multi is running on
its own without 1Mc input from the crystal, or is simply ignoring the sync
signal.  

I found and purchased two spare calibrator modules, one with a crystal
(untested).  Haven't had the time to put a scope on it and try to understand
what's happening.  Hopefully soon. In the meantime, the R-390A is back on
the table.

Too much work in the queue and too little time :-)

Grant/NQ5T

> -----Original Message-----
> From: roy.morgan at nist.gov [mailto:roy.morgan at nist.gov] 
> Sent: Sunday, November 18, 2007 12:30 PM
> To: Grant Youngman
> Cc: r-390 at mailman.qth.net
> Subject: RE: [R-390] A Few R390A Issues Zero Adjust
> 
> Quoting Grant Youngman <nq5t at tx.rr.com>:...
> > I currently have the R-390 on the bench because of a 
> problem with the
> > calibrator module (still undiagnosed
> 
> Grant,
> 
> I remember a comment on the list earlier that the R-390/URR 
> calibrator uses a
> 1MC crystal, and the mulitvibrator is running if synched 
> correctly at 100 kc. 
> So, the adjustment of the multivibrator is somewhat critical.  If the
> calibrator is producing about 90 kc or 110 kc, then this is 
> the direction to
> look in.
> 
> The 1MC crystal will be less expensive to replace (new) than 
> a 200 kc one as
> used in the R-390A/URR.  If it's the crystal, you may well 
> find a workable
> substitute for very little.  I don't know what might happen 
> if you put a garden
> variety crystal into that oven, but of course you could make 
> a plug-in adapter
> to use any crystal from an octal tube base.
> 
> Roy
> K1LKY
> 
> Roy Morgan
> 13033 Downey Mill Road
> Lovettsville VA 20180