[Hallicrafters] SX 101A hum

[Bob Macklin]

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
>
>
>
> ______________________________________________________________
>