[R-390] Audio HUM WAS: B+ short in RF deck

[Barry]

Does this receiver have the fuse in the B+ line?  If not, can you measure the load on the B+ supply to ensure it's not more than the rated load?

Regards,
Barry - N4BUQ

----- Original Message -----
> From: "Dennis Wade" <sacramento.cyclist at gmail.com>
> To: "R-390 HF Receiver List" <r-390 at mailman.qth.net>
> Sent: Friday, January 2, 2015 3:13:05 PM
> Subject: Re: [R-390] Audio HUM WAS: B+ short in RF deck
> 
> Happy New Year all,
> 
>         An update to the audio him issue.  Received replacement caps for
> C603 and 606 and replaced the 20 year old caps on the headers I made back
> when I got the receiver.  Audio hum remains at previous levels.
> 
>         Placing a 47 mf cap across the B+ reduces the hum drastically, as
> before, and another 47 mf cap in parallel drops the him down to about 160
> mv on a 195 volt B+ line.
> 
>         Obviously, something isn't working right.  I did check the dc
> resistance of the inductors which is within spec.  Nothing obviously over
> heating.  I am very tempted to wire in the additional C.
> 
>         Short of swapping in another inductor(s), anything else I can
> check?  The rectifiers are good.
> 
>                       Dennis
> 
> On Sat, Dec 13, 2014 at 8:46 PM, Roy Morgan <k1lky68 at gmail.com> wrote:
> 
> >
> > On Dec 13, 2014, at 11:37 PM, Dennis Wade <sacramento.cyclist at gmail.com>
> > wrote:
> > >
> > > I did find a 10 uf @ 450 (after, of course), and hung that across,
> > dramatic reduction in hum.
> > >
> > > Looks like I'll be ordering some caps…
> >
> > BINGO  I think you’ve got it.
> >
> > Check hayseed hamfest for plug-in caps that will do the job.
> >
> > Roy
> >
> > Roy Morgan
> > RoyMorgan at alum.mit.edu
> > K1LKY Since 1958
> >
> >
> 
> 
> --
> "If they trust you, it is an extraordinary privilege, and you simply can't
> abuse it."
>       - A. Alan Post  1914-2011.  California Legislative Analyst 1949-1977.
> 
> -------------------------
> Dennis L. Wade
> KG6ZI
> Carmichael, CA
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