[AMRadio] DX-100 / Apache modifications on the Web

[rbethman at comcast.net]

I have to agree with Mahlon implicitly.  My Apache has under gone these
mods - PLUS the Russ WB3FAU feedback mod.

The 40 mtr "critical" ears, and the monitor scope bear out the results.

No more distortion - beautiful audio, and control through feedback make
operating a grand experience!

Bob - N0DGN  Craf-T-Bob  (Because I love Hallicrafters!)
Apache(2), Mohawk(2), HT-32A, SX-99, SX-101 mk III, R-390A
EAC, R-390A Collins, DX-60 w/HG-10


----- Original Message -----
From: "Mahlon Haunschild" <mahlonhaunschild at cox.net>
To: <amradio at mailman.qth.net>
Sent: Monday, April 15, 2002 10:15 PM
Subject: [AMRadio] DX-100 / Apache modifications on the Web


> All,
>
> What with the recent discussion on the subject of Apache modifications
> on the list, I thought I would share the links to the source material I
> found on the Web for this subject when I embarked on re-working my
> Apache last year.
>
> ------------------------------------------------------------------------
> The W3SCC / W3YGC Apache audio circuit can be found at:
>
> http://www.amfone.net/AMPX/71_2.gif
>
> I applied this circuit to my Apache without change, with great success.
> The whole thing can be built on a strip of perfboard and wired into the
> Apache in place of the existing audio circuit, making this mod easily
> reversible.  Note that the heater pins of the 12BY7A are mis-labeled on
> the diagram (no biggie).
>
> Andy Bell, KC4FCU, wrote some comments in an old issue of the AM
> Press/Exchange outlining some simple changes:
>
> http://www.amfone.net/AMPX/114.html
>
> The Self-Modulated Screen Grid by Bacon, WA3WDR, advocates moving the
> Apache final amplifier screen supply point from the output of the mod
> transformer to the HV-input-side.  This allows the screens to
> self-modulate because of the impedance of the screen dropping resistor.
> This also gets approx. 20 mA DC out of the modulation transformer
> secondary, which can only improve its linearity:
>
> http://www.amfone.net/AMPX/98.htm
>
> Factory mods/updates for the Apache and SB-10 SSB adapter (transcribed
> from the original Heath notes by VE3FAB).  Note that the final
> amplifiers in early Apaches weren't neutralized; unfortunately,
> retrofitting this in the factory way requires a different mode switch
> wafer:
>
>
http://www.mines.uidaho.edu/ftp/pub/Glowbugs/BAarchives/heath.apache.bulleti
n
>
> DX-100 Modifications by Ed, AA8TV.  Useful material because the DX-100
> modulator is similar in concept to the Apache's.  This write-up and the
> following one got me to thinking of the remaining mods (few though they
> may be) that I might perform on my Apache.  Of particular interest is
> his negative feedback circuit:
>
> http://www.amwindow.org/tech/htm/dx100/dx100.htm
>
> WA1HLR's DX-100 Modifications (again, included for the same reason as
> the preceding link):
>
> http://www.amwindow.org/tech/htm/dx100.htm
>
> DX-100 Screen Optimization by Dean McGorill (again, included here for
> the sake of completeness):
>
> http://www.amwindow.org/tech/htm/scrnmod.htm
>
> ----------------------------------------------------------------------
>
> As I have previously written I can personally attest to the W3SCC /
> W3YGC Apache audio circuit as well as replacing all selenium rectifiers
> with silicon parts and doubling the value of all filter capacitors.  My
> Apache ROCKS on AM now!  Because it's so good at the moment, I've been
> reluctant to open it up again to apply a negative feedback circuit, but
> two friends of mine have done this to their Apaches and have spoken
> highly of it.
>
> A few of other thoughts:  I use 6146Bs in my Apache without any
> problems, but mine has the neutralization update.  Svetlana 6CA7/EL34s
> work fine in lieu of the stock (unobtainable) Mullard tubes.  Do be a
> pal and operate the transmitter and modulator within the manual's
> specifications.
>
> HTH.  regards,
>
> Mahlon - K4OQ
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