[AMRadio] Re: Apache audio Real good

Mahlon Haunschild mahlonhaunschild at cox.net
Mon Apr 15 23:06:47 EDT 2002


The DX-100 modulator description that appears in the manual on BAMA
bears out your comments (see the bottom of
ftp://bama.sbc.edu/downloads/heath/dx100/dx100p05.gif for the details). 
Similar description does not appear in the Apache manual.  Indeed, the
Apache manual specifically states that the modulation transformer is
matched to the modulator tubes.

The DX-100 schematic notes that the primary impedance of the modulation
transformer is 8000 ohms, p-p.  The Apache schematic notes that the
primary impedance of the modulation transformer is 11000 ohms, p-p. 
Secondary impedances are (nearly) the same, and the plate voltage is the
same, and the modulation transformers are the same, and there aren't any
other components left unaccounted for, so I wonder if the tubes are the
answer.  Gotta think about this one....

In the DX-100 there is a .02 uF capacitor connected across the
modulation transformer secondary to roll off the unwanted high
frequencies.  Something like this (maybe .01 uF instead) might be a
good, neighborly thing to install in an Apache equipped with a W3SCC
audio circuit.


Mahlon - K4OQ

> Date: Mon, 15 Apr 2002 11:03:04 -0400
> From: Gary Schafer <garyschafer at attbi.com>
> Organization: CEMCO
> To: amradio at mailman.qth.net
> Subject: Re: [AMRadio] re: Apache audio Real good
> Reply-To: amradio at mailman.qth.net
> I don't know about the Apache but the DX-100 and Viking 2 have the mod transformer ratio set so that the modulator tubes go into peak limiting before 100% modulation is reached. This is a form of high level
> clipping. Most transmitters like that did the same thing. It would be interesting to know if the mod transformer in the Apache has the same turns ratio as the DX-100. Although it may still be different because
> I think that the DX-100 did not use 6146B's in the finals as the Apache did. The Apache was designed to run at higher power than the DX-100?
> 73
> Gary  K4FMX
> "WILHITE, JIM" wrote:
> > I am not sure about the Apache manual, but the DX 100 manual says that the modulation transformer is mismatched.  I am guessing that since the design is pretty much the same that holds true for the Apache.
> >
> > 73  Jim
> > de W5JPW
> >
> > Russ:
> > I'm curious as what Apache manual you're reading. I can't find any
> > reference to where Heath engineers intentionally mismatched the
> > modulation transformer to force more audio through it. Are you refering
> > to the fact that they designed it for class AB2 audio or some other
> > evidence. See page 7, paragraph 7 of the manual: "The modulation
> > transformer provides the proper match between the modulator output
> > impedance and the load impedance."

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