Heathkit GR-54 audio hum fix

[Ed Van Krevelen]

I have recently begun buying and repairing Heathkit radios.  When I was a
teenager some 35 years ago my dad gave me a Heathkit GR-64 for Christmas.
That radio I assembled has long been lost.  My dad and two of my bothers are
radio amateurs.  I never did get my license but I did go on be become an
Electronics Technician after my four year hic in the Navy.  I am now a
Computer Analysis Programmer and thought it would be fun to get back to
doing my first love, electronic repair targeted at older tube radios.

I have purchased both a GR-64 and GR-54 from Ebay.  I have completely
re-tubed and realigned both receivers and made some minor repairs.  When I
received the GR-54 it had an intermittent audio output tube (6HF8).  I
bought a replacement and after inserting it, the radio had a very loud hum.
 I first thought it was a bad tube so I ordered another.  It also had the
same level of hum.

Next I did a Google search and found this wonder source of information and
tried all of the recommendations found here in, to no avail.  The hum
persisted.  I noticed the HW-16 was using the same audio output tube and
circuit but with far different values and an added C87 on the input of the
second stage.  So I rebuilt the GR-54 output using HW-16 circuit values.  I
also used the increased value for HW-16 C87 to .002.  This finally cured the
hum.  The radio has absolutely no hum for both internal and external
speakers.  The audio output performance is also very good.

So it would seem that the circuit design used in the HW-16 is superior to
the original one used in the GR-64.

This appears to be the BEST site for information regarding Heathkit and
wanted to share what I had found with all of you.

Best regards,
Ed Van Krevelen
Wasilla, Alaska – 35 miles from Anchorage.

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