[Boatanchors] SX-122 hum and noise

[Ian]

Byron,

You speak of a "new filter cap"...  I assume that means you have replaced
all sections (3) of C99???

What about C97 and C77?

Have to loosened and retightened all mounting hardware to try to make sure
all grounds are made securely?

Until you do that I'd not go further.

A scope or even an audio signal tracer might be worthwhile to see if you can
find where the hum is being introduced.

Ian, K6SDE

| -----Original Message-----
| From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
| bounces at mailman.qth.net] On Behalf Of Byron Tatum
| Sent: Thursday, March 25, 2010 7:45 PM
| To: Boatanchors at mailman.qth.net
| Subject: [Boatanchors] SX-122 hum and noise
| 
| Hello-
|     I am trying to root out two types of objectionale noise coming out of
audio channel on
| mySX-122. The receiver has a  new filter cap, that I have ruled out, as
there is no ripple
| on the B+. I recently installed shielded leads on the AC power run from
rear panel to front
| panel on/off switch. It did not seem to help.
|         1. A constant hum is present in the audio, it is not too terribly
objectionable but quite a
| bit more than any of my other tube receivers.
|         2. A lower pitched hum is added in when the BFO is turned on, and
this hum is
| noticably louder. The hum does not change in any way as the BFO is tuned.
|     I believe hum in the audio has been a common problem with these sets,
does anyone have
| any advice or info?
|                                                         Thanks, Byron.
|