[R-390] EAC power hum

[Les Locklear]

EAC Power Supplies (bot all ef them) have a well documented mechanical hum. Insulate the hold down screws, or leave them loose. Short of anything else, replace it.

YMMV

Les Locklear
Gulfport, Ms.
Dx'ing since '57


  ----- Original Message ----- 
  From: Steve Toth 
  To: r-390 at mailman.qth.net 
  Sent: Friday, January 08, 2010 12:24 PM
  Subject: [R-390] EAC power hum


  Just powered up a late model EAC I purchased and it has a loud mechanical hum when cold. It's a complete EAC with all EAC decks. I compared it with my Collins and Motorola and it is much louder than either one.

  I looked through the "Pearls" and used an insulated screwdriver to listen to components and the hum seems to be coming from the transformer (to a lesser extent) and the line power filter (to a greater extent). The 25Z5's both check good on the TV-7 with no shorts. I haven't checked the rest of the tubes yet. I also haven't swapped the power deck from either of the other receivers yet. 

  I loosened up the six power supply mounting screws and that did seem to decrease the hum level to an almost acceptable level by apparently reducing the sound conduction from the power supply to the chassis, but I'm not real keen on the idea of leaving the mounting screws loose.

  What has been found to be an acceptable way of decreasing the sound conductivity and retaining the mounting and grounding integrity on the power supply?

  I would like to keep all the decks EAC. What has the group decided is the best cure? IEC approved line filter? (don't flame me on that one) Different power supply module? Replace the power transformer? 

  Or, just live with it - Hey!, it's an EAC! .







  -- Steve 
  Woodinville, WA




        
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