[Boatanchors] NRC Set: Another Programmable Osc. Success.

[W2HX]

Dave, very nice idea.  Curious, I would imagine the 6705's current consumption would be pretty predictable. Why not a simple resistive voltage divider for VCC instead of a dc-dc converter?
Thanks
Eugene


-----Original Message-----
From: Boatanchors [mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of David Stinson
Sent: Sunday, June 26, 2016 12:39 PM
To: milsurplus at mailman.qth.net; boatanchors at mailman.qth.net
Subject: [Boatanchors] NRC Set: Another Programmable Osc. Success.

Got the little Northern Radio Company type 450 working well on the four most popular AM freqs here in North Texas:  3885, 3890, 7160 and 7290. 
Will soon add 3880.  25 W unmodulated carrier out into 50-Ohms on all freqs.

While I was able to scrounge or etch crystals for three of the four freqs, the 6705 Receive (7160-455KC IF = 6705) eluded me.  I tried twice to etch a 6650 CR-1 blank up to 6705, but etching with WHINK can be unpredictable.
In both cases I etched them too far and CR-1 blanks do not "rubber down" very well.  They'll go dead on you quickly.  So I got tired of fighting with it and ordered a 6705 programmable oscillator for $4.10 from Digikey.
Installed it in an empty FT-243 holder.
https://goo.gl/photos/3xoam8dD2oHcDTjr6

I've written many times about this so won't go
into great detail.   Since this 1963 set uses
a germanium-transistor receiver, it doesn't need the heavy LO injection some of my earlier tube sets have needed.  The output of the Prog. Osc.
is coupled directly to the RX Xtal socket with a 100 pFd cap, rather than the .004 uFd used in my tube sets.  The primary 13.5 VDC supply is bucked-down to regulated 5 VDC with one of those nifty little DC-DC boards you can get for cheap on Ebay.  
.1 uFd bypass across Vcc and GND.
Connected the juice, aligned the channel and away we go.  Workie goodie.
https://goo.gl/photos/5kzkZ93ijw3YZ3Dp6

I have no birdies from the little DC-DC thingie, but if you do, glue a little piece of ferrite or steel on top of the tiny inductor and the birdie will fly away.

73 OM DE Dave AB5S

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