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

[Dennis Wade]

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