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

[Dr. Gerald N. Johnson]

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. I added an 
IF output jack and had it on a scope. With it switched to AM with just 
IF transformers, the power line noise showed peaks for every voltage 
peak of both polarities for 6 phases (a delta-Y substation transformer 
was nearby) with gaps between then. When the filter switched in there 
was just a solid envelope of noise based carrier. A few years later I 
integrated a BC-453 Q-%er and converter into the station so I could run 
it and the S-line at the same time. During stormy weather on 75, the all 
IF transformer BC-453 allowed solid copy while the S-3B made for very 
difficult or no copy. The Collins filters used in Yaesu these days 
perform much better with signal transients.

That makes me lean towards the receivers without mechanical filters for 
AM, like the R-390, the 75A-1 or 75A-2, the S-line without the 
mechanical filter on AM, or 51J but not the 51J-4. The skirts won't be 
as steep with the IF transformers but the AM quality will probably be 
better than that vintage mechanical filter. Most often a 6 kHz filter 
was proposed for AM, not an 8 kHz which inherently limits the AM audio 
to less than 3 kHz, OK for communications, but poor for music.

Note that there were also a few 75A-2A that were factory modified to 
take the 75A-3 mechanical filters.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.

On 7/20/2015 9:41 AM, Glen Zook wrote:
> Many consider the 75A-1 to be the best for AM reception.  To me, it is a "toss up" between the 75A-1 and 75A-2.  The 75A-3, like the 75A-4, has a mechanical filter and that definitely "narrows" the response.
> I do have an 8 kHz filter in my 75A-4 and that does help with AM.  However, the 75A-1 and 75A-2 are still better.  By the way, I do have all 4 of the "A" line receivers:  75A-1, 75A-2, 75A-3, and 75A-4. Glen, K9STH
>
> website:  http://k9sth.net
>
>
>       On Sunday, July 19, 2015 9:24 PM, John King via Collins<collins at mailman.qth.net>  wrote:
>
>
>    Which of the Collins 75A1, 75A2, 75A3 and 75A4 communications receivers is the "best" station receiver for amplitude modulated amateur radio reception? Is there a commonly accepted conclusion held among Collins receiver owners? The narrower bandpass of the 75A4 receiver might give it a negative for AM reception and an advantage for SSB reception??
> This is a serious request for input and your input based on personal knowledge and experience will be greatly appreciated. Thanks and 73, John, K5PGW
>
>
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