[Collins] Suggestion of best 75A receiver for AM reception

[Joel Hallas]

FWIW, before I found a 6 kHz mechanical filter for my 51J4, I just used a
coupling capacitor to bypass it (perhaps with a resistor on one or both
sides as needed, I forget) and plugged that into the socket. The AM
broadcast reception was quite nice. I eventually found a 6 kHz filter from a
different 500 kHz IF radio and adapted it -- much better on 75 AM, but not
as good for broadcast.

So, if you have an A3, A4 or J4, all is not lost, use a 0.01 uF capacitor in
place of the 6 kHz mechanical filter and you will get the hi-fi(ish)
reception you seek, if not the QRM reduction.  

Regards, Joel Hallas, W1ZR
Westport, CT


-----Original Message-----
From: Collins [mailto:collins-bounces at mailman.qth.net] On Behalf Of
billriches
Sent: Monday, July 20, 2015 12:31 PM
To: geraldj at netins.net; collins at mailman.qth.net
Subject: Re: [Collins] Suggestion of best 75A receiver for AM reception

I am fortunate to have an R-725 - the Servo modified R-390A and a 390A in
the same rack and do notice the difference in noisy reception.  725 is
quiet!

(The R-725 was a modified R-390a with an R-390 IF deck. The mech filters
rang and sang and were unusable for diversity direction finding work.  I
believe only about 1000 of the r-725s were built.)

73,

Bill, WA2DVU
Cape May 

-----Original Message-----
From: Collins [mailto:collins-bounces at mailman.qth.net] On Behalf Of Dr.
Gerald N. Johnson
Sent: Monday, July 20, 2015 11:02 AM
To: collins at mailman.qth.net
Subject: Re: [Collins] Suggestion of best 75A receiver for AM reception

I suspect the mechanical filters of that era, like those in the S-line rang
like a bell when hit by lightning static and power line noise. I know the
standard filter in my new 75S-3B did that in 1964. 


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