[AMRadio] 51J3 or 75A3?

Mike Sawyer w3slk at uplink.net
Sat Mar 4 16:09:44 EST 2006

Boy, I'll concur. I have a 75A3 that W3HM did for me and the audio sucks. I 
would go for a National or an older Hallicrafters. Brett, where did you pick 
up the Kiwa filters? I would like to try something along that line just so I 
can say I opened the audio. I have the 3.2Kcs mechanical filter and it 
sounds like crap.

----- Original Message ----- 
From: "Brett gazdzinski" <brett.gazdzinski at verizonbusiness.com>
To: "'Discussion of AM Radio'" <amradio at mailman.qth.net>
Sent: Saturday, March 04, 2006 3:50 PM
Subject: RE: [AMRadio] 51J3 or 75A3?

If you was to ask me, none of the below sounds real good on AM.

They sound lots better if you take audio off the detector.

You also want something that has about a 6kc filter.
Wider is better, but then you get the guys next door.

I know there is a wide range of what people think sounds good,
some people think a good phone, or a good 2 meter rig sounds good,
or really anything that has under 15% distortion
and goes 300 to 3000...

Some old receivers did have good audio, with push pull output stages
with a good amount of power at low distortion, and a good
frequency response, but collins never made
anything like that as far as I know.

The scott SLRM had a direct coupled driver stage going to push pull
6L6's (actually 25L6's), and sounded very good, it also had a 'hifi'
bandwidth position (16kc?).

Some of the old halicrafters had push pull outputs, SX 17, SX 28
and others, with up to 17 watts out!

AM detectors and the agc action also play a big role, collins
used a simple diode detector most times, not the low distortion
cathode follower type detectors used in some other receivers...

If you must have the collins, I would go for the 75a3, its got
a nicer S meter, and uses a 455Khz IF, the 51J used 500 khz.
You can get nice kiwa filters for anything that runs 455Khz
for $50.00.  Any bandwidth you want.
They work just like mechanical filters, maybe better...

I always thought a 75s1 would make a good AM receiver, replace
the back to back IF cans with a kiwa filter, or put it
between the cans, build a low distortion detector, and it might
make a good receiver in a small package.

I will pick one up someday and experiment on it.
The 75s1 is still reasonable, everyone wants the 75s3 and
the prices are crazy.


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