[AMRadio] 51J3 or 75A3?

Brett gazdzinski brett.gazdzinski at verizonbusiness.com
Sat Mar 4 15:50:01 EST 2006

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.



> -----Original Message-----
> From: amradio-bounces at mailman.qth.net 
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Theo Bellamy
> Sent: Saturday, March 04, 2006 3:05 PM
> To: Discussion of AM Radio
> Subject: [AMRadio] 51J3 or 75A3?
> I am shopping for a receiver to use on AM. I think I want 
> either a 75A3 or a
> 51J3. Which one is best for AM use as far as making pleasing 
> sounds come out
> of the speaker? I used to have a 51J4 and a 75A4, and they worked fine
> (especially the 'J4), but I have heard that the 'J3 may have the best
> sounding audio section for AM. True?
> Thanks,
> Theo K4MO
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