[R-390] R-390A Crystal Product Detector Modification

[gary.biasini at shaw.ca]

Miles,

Good morning.

Below is a link to a document which may be similar to what you have
described:

http://www.treetopcircuits.com/docs/bfomods.pdf

Regards,

Gary

-----Original Message-----
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> On
Behalf Of k2cby at optonline.net
Sent: October 28, 2020 9:03 AM
To: Gary Biasini <gary.biasini at shaw.ca>
Cc: Collins R-390 HF Receiver List <r-390 at mailman.qth.net>
Subject: [R-390] R-390A Crystal Product Detector Modification

My prior email on this subject got truncated - apparently because some of it
was in Italian.

Somewhere in the bowels of the internet I came across a schematic titled
"Fig.-23-Electrical schematic regarding a product detector installed by
Electronic Assistance Co." (My amateur translation from the original
Italian.)  It shows a purported EAC modification that uses the triode
section of a 6U8 as a crystal-controlled BFO and the pentode section as a
product detector for SSB reception.

I assume that this was incorporated in some R-390s exported to Italy
(military or civilian?). 

Was this merely a "good idea" or was it actually implemented? Ever in a US
military version? Has anybody ever run across one of these sets?

One thing puzzles me: There are two crystals (one for USB and one for LSB)
in series-resonant circuit, but the crystals are selected by a new rotary
switch that replaces S-101 (the "BFO" ON-OFF switch). The adaptor itself is
apparently mounted on or incorporated into the AF subchassis. What makes me
curious is that the crystals are connected to the switch by coaxial cables.
There's quite a physical separation between the switch and the oscillator
tube, and it seems strange to me that they would outboard a
frequency-determining element by a cable run. Why didn't they use a couple
of relays?

Comments?

 

Miles B. Anderson, K2CBY
16 Round Pond Lane
Sag Harbor, New York 11963-3821
Phone: (631) 725-4400
FAX: (631) 725-2223

e-mail: k2cby at optimum.net <mailto:k2cby at optimum.net> 

 

 

 

Miles B. Anderson, K2CBY
16 Round Pond Lane
Sag Harbor, New York 11963-3821
Phone: (631) 725-4400
FAX: (631) 725-2223

e-mail: k2cby at optimum.net

 

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