[R-390] EAC power hum

[Craig C. Heaton]

Steve,

First thought which comes to mind, the filter caps in the power supply are
old, dried out, need replaced, etc. Which leads to the issue of to replace,
reform and that stuff. Nuff said there.

Could be issues with the line filter, but it is easy to bypass or remove it
from the receiver and see if the hum is less or goes away.

Regards,
Craig





-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Steve Toth
Sent: Friday, January 08, 2010 10:25 AM
To: r-390 at mailman.qth.net
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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