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

[Barry]

This might help.

www.mumnme.com/pictures/osc1.jpg

www.mumnme.com/pictures/osc2.jpg

www.mumnme.com/pictures/osc3.jpg

www.mumnme.com/pictures/osc4.jpg

www.mumnme.com/pictures/osc5.jpg

Thanks,
Barry - N4BUQ

----- Original Message -----
> From: "Garry Stoklas" <jergar at sbcglobal.net>
> To: r-390 at mailman.qth.net
> Sent: Tuesday, March 13, 2018 4:12:52 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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