[AMRadio] Old Ham, New AM Enthusiast

[rbethman]

Okay,

Here is the inverse feedback info.  I got it from WB3FAU, Russ:

It doesn't have to be all that complicated and really its not even 
necessary.  Anyway,  the inverse feedback on the Apache is pretty 
simple.  You need 2 parts,wire and your soldering tools.  a 500k pot  
hooked up as a rheostat and a hi-voltage
cap about 2kv@ .01uf.  Under the chassis,  you will find a 500 ohm tap 
on the secondary of the mod transformer,  tied to a terminal all alone.

Take one end of that cap and tie it there-  other end of the cap goes to 
one side of that pot- the other end of that pot goes to the cathode of 
the audio driver tube-12BY7.  Thats it for wiring!  Now to adjust 
it-start out with the pot fully closed-  put the transmitter on the air- 
gradually open the pot-  you will reach a point of instability-  turn it 
back  just a little -  thats it!  There should be a big improvement in 
the transmitted audio.  As I said,  some of these guys are going to 
extremes with mods.  Most of us do not have hi-fi receivers so whats the 
point?  There are a lot more tricks to do on the Apache,  do this mod 
first and then decide later if you need to do more.   Russ

AND make DAMN sure you run an oscilloscope or station monitor!  
Otherwise you are running blind!  Wattmeters won't tell the real story!

Bob - N0DGN

On 12/28/2010 2:27 PM, rbethman at comcast.net wrote:
> Larry and crew,
>
> That is a far more drastic method than I was thinking about.
>
> There is an audio mod for the TX-1 by W3SSC and another ham.
>
> The mod and schematic are on the Mods part on AMPhone.net, under mods.
>
> Then for an additional piece of help, the plate mod section uses a .1 
> ufd 1KV disc ceramic and creates negative feedback.
>
> I'll have to find the info in "my" archives as to the precise location.
>
> Bob - N0DGN
>
> ----- Original Message -----
> From: "Larry Szendrei" <ne1s at securespeed.us>
> To: "Discussion of AM Radio in the Amateur Service" 
> <amradio at mailman.qth.net>
> Sent: Monday, December 27, 2010 5:59:39 PM
> Subject: Re: [AMRadio] Old Ham, New AM Enthusiast
>
> On 12/27/2010 1:24 PM, rbethman wrote:
> > Jerry,
> >
> > You are getting good advice - so far!
> >
> > One other made comment regarding the Apache.  It has a "well earned"
> > nickname. * Scratchy Apache *
> >
> > It take a bunch of work reworking the audio circuitry to make it sound
> > like "you" REALLY sound.
> >
> > It also REALLY needs negative feedback added in.
> >
>
> I used to have an Apache. When I bought it, the modulators had been
> converted to triode-connected 6146s driven by outboard audio*. The thing
> sounded very, very good. The only thing that was used from the original
> Apache audio section was the modulation transformer, which isn't a bad
> piece of iron.
>
> *This is what the audio section looked like:
>   -push-pull tube type audio output xfmr with 8 ohm speaker winding as
> audio input from external audio amplifier capable of at least 5-8W
> output. (original) high-Z primary ends go to 6146 modulator tube screen
> grids, and center-tap of this winding goes to ground.
>   -6146 modulator control grids tied to about -5V bias, well bypassed
> for audio and RF, to put the operating point for the modulator tubes in
> a good place.
>   -6146 plates to each end of mod tranny primary per usual arrangement.
>   - voila! quick and easy good audio for the Apache!
>
> Having said that, though, I agree with Rob about focusing on the antenna
> first, and spend some time on AM before deciding what the  "upgraded" AM
> station will be.
>
> Here are some AM nets up here in the Northeast you might be interested
> in checking into:
>
> AM Carrier Net, Sundays at 8:30AM on 3835 KHz
> Antique Wireless Association Sunday PM AM net, Sundays at 4:00PM on 3837
> KHz.
> Gray Hair Net, Tuesday evenings at 8:00 PM EST (or 8:30PM EDT) on 1945 
> KHz.
>
> 73 and we'll be looking for you Jerry,
> -Larry/NE1S
>
> ______________________________________________________________
> Our Main Website: http://www.amfone.net
> AMRadio mailing list
> Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/
> List Rules (must read!): http://w5ami.net/amradiofaq.html
> List Home: http://mailman.qth.net/mailman/listinfo/amradio
> Post: AMRadio at mailman.qth.net
> To unsubscribe, send an email to amradio-request at mailman.qth.net with
> the word unsubscribe in the message body.
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

-- 
+------------------------------------------------------------------+
|               AM Amateur Radio Operator    NØDGN                 |
+------------------------------------------------------------------+
|               http://home.comcast.net/~rbethman/                 |
+------------------------------------------------------------------+
| Bob Bethman                \\\|///     " The absence of a danger |
|                           \\ ~ ~ //      signal does *NOT* mean  |
| rbethman at comcast.net      (/ @ @ /)      that everything is OK " |
+----------------------o00o---°(_)°---o00o-------------------------+