[Heathkit] Apache TX-1 Audio Mods

[Glen Zook]

Actually, C60 is originally a 0.01 mfd capacitor. 
However, it is a disc ceramic.  An orange drop (this
is not a paper capacitor) does seem to work better at
audio then a disc ceramic.  The other two capacitors
are 510 pf and definitely need to be changed to 0.01
mfd orange drops.

changing C66 will upset the frequency response of the
microphone input circuitry.

The article that appeared in Electric Radio a while
back on the changes to the Apache audio chain can be
found on either of the websites the URL of which are
listed at the end of this message.

Just changing the 3 capacitors and unplugging the 6AL5
clipper tube (you don't have to make any circuit
changes in the clipper circuitry) makes a marked
improvement in the audio characteristics of the
Apache.  After I made these changes the first time
that I checked into the 3880 KHz morning AM net (which
has a number of VERY critical operators as to how the
rig sounds) I got rave reviews from even the most
critical of the operators.  This was using a "stock"
D-104 with the preamplifier bypassed.

The modification takes about 10 minutes to accomplish
and makes a "world of difference" in how the Apache
"sounds" on the air.

Glen, K9STH


--- Robert & Linda McGraw K4TAX <RMcGraw at Blomand.Net>
wrote:

I've noticed in several articles indicating that the
audio coupling capacitors C64, C61 and C60 were
changed to 0.01mfd paper caps.  Originals were disk
ceramic and typically 510 pf.  In looking further at
these changes, I see that the input cap C66 is
original at 0.005 mfd.  Would there be any reason or
benefit to changing this cap to a 0.01 as well? Also,
adding self bias {cathode R and bypass} to the input
stages at V7 and increasing the value of R48 to 4.7
meg should help to clean up the front end.


Glen, K9STH

Web sites

http://home.comcast.net/~k9sth
http://home.comcast.net/~zcomco


	
		
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