[R-390] 390A Squelch info online part II

[Tom Norris]

Slight edit of content, changed file name.  See below. The audio  
module partial schematic is slightly more readable and there is a  
photo of the front corner of the audio module for those who may not  
know where the "optional squelch" was supposed to go.

73

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I did a quick grab of the 390A squelch and wrote a tiny bit about  
it.  Included some of the original schematic so you can see it in  
context.  It picks up its signal from the diode load at pin 11 of J620.
  The circuit is enabled via the function switch at one click past  
cal.  This voltage appears at J619-8.
It simply grounds the audio line via J620 pin 2.  The wiring harness  
for the circuit should be installed in the deck -- even my 1967 EAC  
has it tied off and unused.  Here's the circuit --

http://www.fernblatt.net/A/390A_squelch.zip

Not to be a blasphemer, but it would be mo' easier using fets.   The  
"squelch B+" might need to be messed with in that case. The switches  
do appear to have wiring in that last position, and there is wiring  
in the audio decks, whether the twa' ary meet, I canna say.

Tom NU4G