[AMRadio] Re: Apache and Mohawk mods

[Mahlon Haunschild]

Ron,

I can confirm through second-hand info that the Mohawk modifications
documented in Electric Radio (and alluded to by Bob below) are the bee's
knees.  Makes the receiver into a whole 'nuther radio.  But I can't
attest to this personally because I haven't gotten 'round to restoring
my Mohawk yet.

Now, on the matter of the Apache, I have personal experience.

The Apache's narrow audio passband is that way by design (in those days,
talk power was more important than fidelity).  But it also seems to me
that the manufacturing tolerances on some of the components in the audio
section were pretty loose to begin with, and have gotten worse with
age.  In particular, the low-pass filter in my Apache had a 6 dB cutoff
of something like 1500 Hz, which I found unacceptable.

The heart and soul of my Apache audio modifications I found on the Web
at:

http://www.amwindow.org/tech/htm/w3sccmods.htm

This audio circuit assumes that you will devote due care to limiting the
amplitude of your audio input signal from your microphone or whatever
(since the clipper is bypassed).

Generally speaking, any of the material you find on the Web for the
DX-100 is applicable to the Apache, because the two transmitters are
very similar in design (though I think the Apache is better built and
has a more powerful modulator).  Just apply some common sense.

I don't use a D-104, by the way; I use a Shure 55SH microphone (high
impedance, of course).  Sounds TERRIFIC.  If you use a D-104, do NOT use
the preamplifier in the T-UG8 stand; it is unnecessary.

Power supply issues:  the filter capacitors in the Apache are too low in
value and have probably dried out anyway or become leaky over the course
of time.  I replaced all of them, usually doubling the values.  All
power supplies are now rock steady in all modes of operation (they
weren't before).  Do NOT replace the HV and B+ rectifier tubes with
solid-state equivalents; it is unnecessary and may lead to unpredictable
operation due to the higher voltages.  DO replace the three selenium
rectifiers in the two bias supplies with silicon rectifiers (you can
simply wire the silicon units across the selenium parts).  This change
alone does wonders to improve the regulation of the two bias supplies. 
PLEASE replace the two-wire line cord with a three-wire grounded line
cord & suitable fuse.

Don't give up on the Apache and, especially, the Mohawk.  Both can be
made into first-class radios; the Apache in particular is much-maligned
and, if you do as I suggest above, is capable of incredible audio
performance.  The Mohawk will require substantially more work to make
right, unfortunately.  Especially if you set out to
temperature-compensate the VFO.

regards,

Mahlon - K4OQ

.
> 
> Message: 4
> Date: Mon, 08 Apr 2002 21:46:23 -0400
> From: rbethman at comcast.net
> Subject: Re: [AMRadio] re:  Apache and Mohawk mods
> To: amradio at mailman.qth.net
> Reply-To: amradio at mailman.qth.net
> 
> Go here to search past issues with Mohawk mods improving overload and AGC
> issues.
> 
> http://www.qsl.net/n9oo/ersearch.html
> 
> Contact Barry Wiseman - Publisher/Editor at er at frontier.net for back issues.
> 
> Bob - N0DGN
> 
> BTW:  I have two Mohawks and two Apaches.
> ----- Original Message -----
> From: "Ron Samchuk" <samvideo at escape.ca>
> To: <AMRadio at mailman.qth.net>
> Sent: Monday, April 08, 2002 7:14 PM
> Subject: [AMRadio] re: Apache and Mohawk mods
> 
> Hi Everyone.
>     I was fortunate to obtain both the Apache and Mohawk pair in very good
> condition.  They both work, but the audio level is low and frequency
> response is limited on the Apache.  I was also hoping for a little better
> performance on the Mohawk receiver.  I would appreciate any and all comments
> on improvements and/or modifications on this classic pair.  Thanks in
> advance for your help.  Ron VE4SR