[Hallicrafters] Power transformer and capacitor replacement

[Misic, George J.]

The tolerance on BA filter capacitors is usually +80 / -20%, so your plan of going up to the next NEMA 20% standard value will be fine.  The series resistance of a vacuum tube rectifier prevents the transformer from seeing anything too terrible from a filter reasonably close to the original value.  73.

George KE8RN

-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net]On Behalf Of Waldo
Magnuson
Sent: Wednesday, August 31, 2005 4:13 PM
To: hallicrafters at mailman.qth.net
Cc: Waldo Magnuson
Subject: [Hallicrafters] Power transformer and capacitor replacement



Power Transformers in our boat anchors are a precious component.  Usual 
practice in restoring or returning to service one of these receivers is 
to replace the power supply section electrolytic capacitors.  Several 
Hallicrafters have capacitor input for the power supply filter (SX-28, 
SX-42, SX-71, SX-100, SX-111, etc.).  The value for the first capacitor 
in the filter is usually 30, 40, or 60 uf.  The capacitors from AES 
that I have been using come in values of 22, 33,47, or 100 uf.  I have 
been in the habit of replacing these capacitors with the next higher 
value (ie. 47 in place of a 40 uf).  I read in Langford-Smith that 
capacitor input filters (as opposed to choke input filters) can reflect 
a terrible heating wave shape to the power transformer.  The higher the 
value of the capacitor, the worst the heating.  So, perhaps a good 
practice might be to replace the first capacitor with a value no higher 
than listed in the parts list and maybe even go to the next lower value 
(33 instead of 40 uf).  Your thoughts on the subject?
73,  Skip Magnuson  W7WGM

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