[Boatanchors] Interminable Hum!

[Bry Carling]

IF touching the shield on that 6AW8 reduces the hum, try touching the chassis. Does that 
reduce the hum?

If it does, then I think you may have a grounding problem.

Does your radio have an old style  two wire plug? Try reversing the plug.

Does your radio have a THREE-wire AC cord on it? If not, you should replace it with one that 
does. That way you can have a proper safety ground and a better AF/RF ground than 
whatever path it is finding now.


On 31 May 2013 at 8:27, Rinkie Pollack wrote:

> I have an R55A which has had the same  problem.  If I remember, it
> was a bad ground somewhere.  That's what I'd check first.  Don't
> just tighten the screws; remove and clean under them
>  
> Ron K2RP
> 
> --- On Fri, 5/31/13, Wilson <infomet at embarqmail.com> wrote:
> 
> 
> From: Wilson <infomet at embarqmail.com>
> Subject: Re: [Boatanchors] Interminable Hum!
> To: AWFremmer at aol.com, boatanchors at puck.nether.net
> Date: Friday, May 31, 2013, 8:00 AM
> 
> 
> Tack a cap across the filter sections, especially the last one.
> Independent of volume suggests it's on the power to the output
> amp.
> 
> WL
> 
> -----Original Message----- From: AWFremmer at aol.com
> Sent: Friday, May 31, 2013 10:53 AM
> To: boatanchors at puck.nether.net
> Subject: [Boatanchors] Interminable Hum!
> 
> Fellow Collectors/Restorers,
> 
> Decided to swallow my pride and come to the experts for  help.  I
> have an
> Allied Knight
> R-55A with a hum problem that I've been unable to  resolve.  I think
> I've
> isolated the source to the preamp  tube, 6AW8.  Swapping the preamp
> tube with
> the amp tube does not help.  When touching the shield of the tube,
> before
> it gets too hot to hold, I can  diminish the hum but not eliminate
> it.The can
> electrolytic runs cool to the  touch even with the radio on for
> hours.  I
> don't own a capacitor checker  but the usual ohmmeter test on all
> four
> sections results in the expected  downward defection and slow upward
> return to a
> high value of resistance.   The hum is independent of the volume
> control
> setting and the receiver plays  strongly enough that the hum is
> simply an
> annoyance but one which I can't  stand.  All screws have been
> snugged up.
> 
> A search of the Internet came up with the following web site,
> _www.ohio.edu/people/postr/bapix/r55a.htm_
> (http://www.ohio.edu/people/postr/bapix/r55a.htm) .   Rich, KB8TAD
> appears to have had the same problem but his solution,
> running a  ground wire from the preamp socket to another point on
> the
> chassis did not  help.
> 
> I also own the R-55 which does not exhibit this  problem.
> 
> Suggestions?  And many thanks in advance for any  help.
> 
> 73, Alan - KB2HEI
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