[Hallicrafters] SX 101A hum

[Bob Macklin]

If the hum is there with the output tube removed then the only path is
induction into the output transformer.

If you are using modern LO-Z headphones connect them to the speaker output
instead of the headphone jack. Then see how the audio level works.

Bob Macklin
K5MYJ
Seattle, Wa,
"Real Radios Glow in the Dark"
----- Original Message -----
From: "Bob Macklin" <macklinbob at msn.com>
To: "David Franklin" <dfranklyn at mindspring.com>; "Andy Bullington"
<abullington at comcast.net>; <hallicrafters at mailman.qth.net>
Sent: Tuesday, February 05, 2008 10:28 AM
Subject: Re: [Hallicrafters] SX 101A hum


> One of the first questions is does the hum change with the audio level. If
> so it is introduced ahead of the volume control. If not it is after the
> volume control.
>
> Bob Macklin
> K5MYJ
> Seattle, Wa,
> "Real Radios Glow in the Dark"
> ----- Original Message -----
> From: "David Franklin" <dfranklyn at mindspring.com>
> To: "Andy Bullington" <abullington at comcast.net>;
> <hallicrafters at mailman.qth.net>
> Sent: Tuesday, February 05, 2008 9:55 AM
> Subject: Re: [Hallicrafters] SX 101A hum
>
>
> > Andy,
> >
> > When you added the three wire line cord did you tie the ground lead to
the
> > chassis?  If so I do not see how it is causing a problem.  To be sure,
use
> > an isolation plug and see if it helps. Since you have replaced all of
the
> > capacitors, here are a few other things to try:
> >
> > 1. Replace the .01 mfd capacitor from one side of the line to the
chassis
> if
> > you haven't already.  (C92)
> >
> > 2. Pull all of the tubes and see if you still hear the hum.  Sometimes a
> > filament can be shorted to the cathode inside the tube.  The tube may
work
> > fine but it will cause hum. If the hum goes away replace the tubes one
at
> a
> > time starting with the rectifier.
> >
> > 3. If you still hear hum with all of the tubes removed you may have a
bad
> > ground somewhere around the audio output.  Check all connections to the
> > chassis especially the tube sockets to make sure there is good contact.
> >
> > 73,
> > Dave
> > W4DEF
> >
> > ----- Original Message -----
> > From: "Andy Bullington" <abullington at comcast.net>
> > To: <hallicrafters at mailman.qth.net>
> > Sent: Tuesday, February 05, 2008 10:18 AM
> > Subject: [Hallicrafters] SX 101A hum
> >
> >
> > It's winter project time so I've decided to revisit my SX 101A. I've
> > realigned it with good results but on using headphones I'm noticing an
> > annoying hum. It doesn't seem to be a tube , there is a 60 cycle hum
even
> in
> > standby mode. Using a speaker the hum isn't as noticeable but still
there.
> > The overall audio sound is very smooth and better than my NC303 but the
NC
> > 303 is hum free. I've long ago replaced all the paper caps and
> electrolytics
> > and also some out of spec resistors. At the same time I did all that
work
> I
> > replaced the power cord with a 3 prong. I'm wondering if I did that
wrong.
> > Any help for a poor technically challenged musician would be much
> > appreciated. Here's where I stand: I get hum even in standby or with the
> > audio turned all the way down or the audio tubes removed. It's not run
you
> > out of the room hum, but it shouldn't be there. Is it something in the
> power
> > supply? Thanks in advance.
> >                      Andy W1AWB
> >
> >
> >
> > ______________________________________________________________
> >
>
> ______________________________________________________________
>