[R-390] 60 Hz Hum Output from R-390A IF Module

[David Wise]

Not to encourage you away from Roger's recommended environment,
but an extender _would_ give you entrée to substitute DC on
the heaters etc.  That would tell you Right Now whether it's
heater, B+, or whatever other weird thing it might be.
That wouldn't get you all the way home, but it would at
least partition the problem.

Dave Wise

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Jon Schlegel
Sent: Tuesday, May 05, 2009 4:03 PM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] 60 Hz Hum Output from R-390A IF Module

Hi Roger,

Thanks for the good ideas on grounding.  Some efforts to improve 
grounding on the extender have dropped the hum to about 33 dB below 
30% modulation.  Not too awful bad.  My next step will be to put the 
module back into the chassis as you suggest and I expect hum level to 
improve from that.  Guess I wasn't ready for the sensitivity to the 
extent that I'm seeing.  I can only guess that it's mainly all that 
heater current finding it's way back to home plate any which way it can.

I think the extender cable effort is worthwhile since I have been 
able to identify some sensitive hum entry points and this my lead to 
possibly doing some things to help desensitize the module to the hum.

I'm guessing that the bypass caps are ok as I replaced all the usual 
suspects with orange drops.  Ground point corrosion could still be an 
issue so I'll check into that.

Thanks again and regards,
Jon


At 05:58 PM 5/5/2009 -0400, Flowertime01 at wmconnect.com wrote:
>Jon Schlegel,
>
>Are you having any luck with your hum in the If deck?
>
>I am first going to suggest you drop the extender cable and get the IF deck
>back into the receiver. Back when, any test that was not all things in
>place was just a distraction. When being defined as 1968 to 1975. If