[AMRadio] Heath Apache symptoms


sbjohnston at aol.com sbjohnston at aol.com
Wed Jan 7 21:47:29 EST 2009


When working on Heathkit equipment, always suspect the resistors.  The 
combination of the type or quality of resistors used byt Heath, with 
the passage of many years, results in quite a few of their resistors 
well out of tolerance, or far up or down in value, or even changing 
resistance under load.

Steve WD8DAS

sbjohnston at aol.com
http://www.wd8das.net/
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-----Original Message-----
From: John King <k5pgw at yahoo.com>
To: amradio at mailman.qth.net
Sent: Wed, 7 Jan 2009 6:03 am
Subject: [AMRadio] Heath Apache symptoms










Hello, fellow AM folks! I would like to hear from those intimately 
familiar with
the Heath Apache.

I think my Apache needs some TLC. It is working and gets good reports 
on
strength and audio, however:

I note that when keyed up, after loading and dipping the finals, that 
the plate
current starts out lower than the tune up and then starts creeping up. 
My
experience over 50 years as a Ham has convinced me that creeping plate 
current
is usually a sign of screens in the final tubes going bad. In fact I 
once had a
Hallicrafters HT 32B that had creeping plate current when the 6146 tube 
screens
began  going bad. In fact, if I didn't increase the bias on the tubes, 
they
would eventually "run away" and self destruct. The finals in my Apache 
do not
"run away" they just go from lower current at tune up and rise to 
slightly more
current than at tune up.

I think that my grid drive is also marginal because it takes all the 
available
grid drive to set it at the rated and desired level of drive. The drive 
control
must be at extreme maximum, fully clockwise. This could be related to 
"creeping
plate current". What do you think?

In addition, I note some downward movement of the plate current of the 
final
amplifier upon modulation. Lack of grid drive may cause this problem if 
I
remember correctly. In addition, I seem to feel that over coupling of 
the output
of the final tank circuit might also contribute to the downward 
modulation? I
recently replaced the 6AQ5 clamper tube but did not readjust the 
circuit after
replacement.

I would like some input from you who have the knowledge and experience 
to
discuss these symptoms. I want to have this discussion before I start 
trying to
wrestle this Green Monster out of its' cabinet. I am not as strong as I 
was when
I became a Novice over 50 years ago. Before you laugh, let me say that 
if you
are LUCKY, maybe you will live to get WEAK!! Hi!! HI!! You may address 
this
issue off the reflector if you prefer. I don't want to bore the other 
members
with a topic that may not be of interest to them. After all, the 
majority of
hams feel that AM is a relic of the past. I enjoy AM, SSB and CW. 
Thanks in
advance and 73, John, K5PGW






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