From: shaun.at.pukekohe@gmail.com   
      
   Once upon a time on usenet Trevor wrote:   
   > On 18/03/2018 11:08 AM, ~misfit~ wrote:   
   >> Once upon a time on usenet Trevor wrote:   
   >>> On 17/03/2018 1:22 AM, audioguymn@gmail.com wrote:   
   >>>> On Friday, July 27, 2001 at 2:34:43 PM UTC-5, MitchSF wrote:   
   >>>>> Hi, I'm almost finished restoring a KLH Model 21.  I replaced   
   >>>>> three transistors on the RF board and it now works!   
   >>>>>   
   >>>>> The only problem left is a hum from the audio board.  I   
   >>>>> disconnected it from the input to the board so I'm sure it's not   
   >>>>> coming from anywhere else.  I replaced the filter capacitor and   
   >>>>> all electrolytics on the audio board and it's a little quieter,   
   >>>>> but still there.  The level of the hum doesn't change with the   
   >>>>> volume control.   
   >>>>>   
   >>>>> Any hints would be appreciated!   
   >>>>>   
   >>>>> Thanks, Mitch   
   >>>>   
   >>>> Hi Mitch. The power supply filters, either of the black color   
   >>>> are/were a common failure item. They should be replaced. However,   
   >>>> note that the positive terminal was marked with the stripe as we   
   >>>> would now associate with the negative terminal. It is also   
   >>>> important that you do not increase the value of these capacitors   
   >>>> as the power supply can't handle the extra in-rush and operational   
   >>>> paramete5rs. Mark - Former National Service Manager, KLH Cambridge.   
   >>>   
   >>> Wonder whether he even still has it 17 years later? :-)   
   >>>   
   >>   
   >> Probably not - at least not with the issue still (however somebody   
   >> might...) It's good to have a knowledgeable person posting here so let's   
   >> not   
   >> be too harsh...   
   >   
   > True, might help someone else, and I wouldn't want to discourage that.   
   > I'm just amazed at how many people answer 20 year old posts because   
   >  they don't even realise it. :-)   
      
   As you likely know it's usually because these days most people don't   
   actually use usenet - they use parasitic web forums that don't delete old   
   posts in an effort to appear to have lots of content.   
      
   Cheers,   
   --   
   Shaun.   
      
   "Humans will have advanced a long, long way when religious belief has a cozy   
   little classification in the DSM*."   
   David Melville (in r.a.s.f1)   
   (*Diagnostic and Statistical Manual of Mental Disorders)   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)