Hum Problem- Off Topic

[Richard Post]

Carl,

Dom N1DM was correct in identifying the probable source of the problem with
this set.   Check out the repair info at the following.  Same set, same
problem.  The tube socket is self-grounding but the rivet holding the
wafers together needs some help.
On topic Heathkit note:  I used my workhorse PS-4 to verify that the hum
was not power-supply related.

<http://oak.cats.ohiou.edu/~postr/bapix/R55A.htm>

73 de Rich KB8TAD

>Approved-By: wb9hgz at CHARLOTTESVILLE.NET
>MIME-Version: 1.0
>X-Priority: 3
>Date:         Sun, 5 May 2002 15:30:00 -0500
>Reply-To: "Carl C. Miller Jr" <bugmarx at ev1.net>
>Subject:      Hum Problem- Off Topic
>To: HEATH at LISTSERV.TEMPE.GOV
>
>Hi All,
>
>I picked up a Knight R-55A receiver recently and it has a serious hum
>problem. The hum is not controlled by the volume control and it is very
>loud. I thought this was a simple matter of replacing the power supply
>filter capacitors, but after subbing in two different sets of caps, no
>change. I changed the rectifier tube just in case, no change. I subbed for
>the other tubes, no change. I checked and tightened the ground connections,
>no change. I looked for shorted parts, bad connections etc. and found none.
>All voltages are within tolerance. The only thing I can see that might cause
>a problem is that the original builder did not believe in using the shortest
>lead lengths possible. There is a veritable forest of components on very
>long leads. This receiver uses point to point wiring. Could it be that these
>extra long leads are picking up hum? or am I missing something else? I
>noticed that moving some of them around, especially those connected with the
>audio section, changes the pitch or tone of the hum.
>Sorry for the off topic post,
>73's
>Carl KA5KAB
>
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