[R-390] R-390A Crystal Oscilattor Mod

[Steve Toth]

My guess: sounds like it might possibly be part of the R-1247 field mod kit for the R390A to enable the R390A to use external high stability oscillators.
- Steve  W7SJT"Always look for a positive solution then Improvise, Adapt, and Overcome"- adaptation of the U.S. Marine Corps motto
"Every day is an opportunity to challenge the achievement of your dreams"
"Success is not final, failure is not fatal.  It is the courage to continue that counts."- Winston Churchill


 

      From: Garry Stoklas <jergar at sbcglobal.net>
 To: "r-390 at mailman.qth.net" <r-390 at mailman.qth.net> 
 Sent: Tuesday, March 13, 2018 2:29 PM
 Subject: [R-390] R-390A Crystal Oscilattor Mod
   
 I wanted to add a R-390A crystal oscillator module to my spares and recently purchased one on eBay. It is a Collins unit s/n 144 and is very clean with a complete set of crystals. I failed to notice the miniature BNC connectors on the back and the extra components on the underside of the front section which consists of a relay, a couple of capacitors and a slug tuned coil in the clamp. There is no access to the slug so clearly it was set to whatever and left. The coax from the connectors go to one pin on the coil and the relay. I'll be testing the crystals (which are all in kc and date coded mid 1950s) in my trusty International Crystal oscillator and then figuring out the schematic of this mod. It was done very professionally. I've search through the tons of material on the R-390A that I've accumulated but have found nothing about modifications to the crystal oscillator module. Pictures of the crystal oscillator module and the modifications can be seen at the following:
www.mumnme.com/pictures/osc1.jpgwww.mumnme.com/pictures/osc2.jpgwww.mumnme.com/pictures/osc3.jpgwww.mumnme.com/pictures/osc4.jpgwww.mumnme.com/pictures/osc5.jpg
Can any of you help identify what the purpose of this modification is/was. If I can't get any information on it, I will remove it.
Garry
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