[Collins] R-388 Y112

[Gerald]

On Sun, 2005-12-18 at 10:27 -0500, Al Parker wrote:
> Hi folks,
>     Stan & I are aware of the function.   I don't want to do the 51-J4
> filter mod., just make the phasing unit work OK.  Problem is that I have a
> bad xtal in mine & haven't found anyone to make one (tho' must admit
> haven't tried all possibilities).  I put out a want on the list a few mo.s
> ago with no results, so Stan & I are looking for alternatives.  Looks like
> the cheap ceramic resonators won't do the job, but at <$1 ea. I'll try one
> after my next Mouser order.  I did pick up a Murata 455kc filter a while
> ago, may try that in an SP-600 to see what it'll do, realizing that it's
> not a filter application as such, and not knowing just what ckt chgs are
> needed.
>     We're looking for thoughts.
> tnx, 73,
> Al, W8UT
> New Bern, NC
> BoatAnchors appreciated here
> http://www.thecompendium.net/radio/
> http://www.hammarlund.info
> 
The ceramic resonator won't have the high Q of the quartz crystal. It
may show some of the same style of response but with a larger spread
between the pass an notch (maybe ten or 20 times wider spacing). The
ceramic filters won't do anything in that circuit. The single crystal
filter was good for its day and not so useful today.

Makers of crystals like ICM and others recently mentioned on this list
should be able to make a suitable crystal. It would be of benefit to
find a maker that made the original crystal because its characteristics
(motional C, motional L, and shunt C) may not be typical of an
oscillator crystal. One history snippet for ICM said they were founded
to make crystals for Collins. I see in the 51J-4 manual that the
military type for the crystal is CR-7. That should be definitive to good
crystal makers.

In the past 50 years there have been 500 KHz surplus crystals. One of
the crystals in the set use for 26 to 32 MHz FM WW2 military radios was
on 500 KHz. Because it made a good calibrator crystal, it became
uncommon except in complete sets long ago.

In theory a maker of crystals should be able to rebuild the original
crystal, but making from scratch is probably cheaper though no where
near the 1952 price of that surplus crystal.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer