[Collins] 75S-1 CW non op question

[Glen Zook]

That is not correct!  There is a jumper, on the mode switch, that puts the USB BFO crystal in the circuit when the mode switch is in the CW position.  However, unless there is a filter installed in the CW position, the receiver will be "dead".

With the 500 Hz mechanical filter, Collins had available a 455.8 kHz optional BFO crystal.  When this crystal was installed, the jumper for the USB BFO crystal is cut and the 455.8 kHz crystal installed in its place.  This is specified in the instructions for installing the 500 Hz mechanical filter:

http://collinsradio.org/archives/manuals/75S-1cwfilter.pdf


For some reason, Art Collins decreed that no 75S-1 or 75S-2 receiver be shipped from the factory with the 500 Hz CW filter installed (and then decreed that every 75S-3 and 75S-3A be shipped with the 200 Hz CW filter installed).  The receiver had to be purchased and then returned to the factory to have the 500 Hz filter installed or the receiver could be shipped to one of the authorized service centers to have the filter installed.  Also, there was a kit available so that the individual receiver owner could do the installation himself / herself.  The instructions in the link were included with the kit.

I own what is probably the only 75S-1 that had the 500 Hz mechanical filter and optional BFO installed when manufactured and it cost a Collins employee his job!  There was an Dallas, Texas, Collins Radio employee who purchased the 75S-1 through the employee purchase plan.  He knew someone at the Cedar Rapids plant and made arrangements to have the filter / BFO crystal installed when the receiver was built.  Shortly after the employee received the receiver, Art found out about it and immediately called the employee into his office.  When Art confronted the employee about the receiver, to avoid Art's wrath, the employee immediately resigned.  That was in like 1959 or 1960.

After resigning, the employee sold the receiver to another amateur radio operator who lived in Garland, Texas (a suburb on the northeast side of Dallas).  This operator already had a Collins 75S-1 receiver so he put this receiver out in his garage where it sat, unused, for well over 40-years.  Then, that operator traded the receiver for some closed circuit television equipment obtained from another amateur radio operator who lived in Terrell, Texas (a town east of Dallas).   At the time, I had an Aerotron 450 MHz repeater with a Motorola duplexer that I had removed from commercial service and the new owner wanted the repeater.  He traded me the 75S-1, a brand new commercial grade wattmeter, and a quantity of cash for the repeater.

When I put the receiver on the workbench, I discovered that it had the CW mechanical filter.  I mentioned this to the person from whom I had acquired the receiver and he said that he would check with the previous owner about the filter.  That is when I learned about the Collins employee losing his job.  The only thing that was "wrong" with the receiver was that, due to being stored in an un-air-conditioned garage for so long, the insulation on the power cord was cracked all along its length.  Otherwise, basically, the receiver was brand new.  I have this receiver paired with my 32S-1 transmitter that I use, occasionally, for SSB operation (my main station is a 75S-3A and 32S-3).

 Glen, K9STH 
Website: http://k9sth.net

      From: Dr. Gerald N. Johnson <geraldj at netins.net>
 To: Rodger Singley <wq9nsc at live.com> 
Cc: "collins at mailman.qth.net" <collins at mailman.qth.net>
 Sent: Friday, September 30, 2016 1:36 PM
 Subject: Re: [Collins] 75S-1 CW non op question
   
Without the CW filter ever having been installed, there is also no 
crystal for the BFO in the CW mode so the product detector has a huge 
signal loss. The only gain working to the speaker is in the two audio 
stages, the detector is one signal break and the lack of filter is a 
second signal break.