[QCWA] Crystal Calibrator.

[Jeffrey D Angus]

The old "frequency meter" everyone remembers from WWII Surplus
is the BC-221.
<http://www.richardsradios.co.uk/bc221.html>
The Navy had one of their own, the LM-13
<http://www.staff.science.uu.nl/~tel00101/FotoAlbum/RadioCorner/Sets/LM13.htm>
Essentially, they are identical.
I ran across the 1.000 MHz crystal for an LM-13 unit. +/- 10 Hz.
Nice crystal, AT cut and in an metal Octal tube type enclosure.

I used a 6SK7 metal octal tube instead of a 7-pin miniature 6AU6,
simply for the esthetics of a tube that matches the crystal holder.
And the rest of the tubes in my Hallicrafters SX-99.

The other day I punched a hole in the back of the chassis near the
antenna connector and mounted an octal socket to plug the crystal
calibration unit into. The pin wiring on the socket matches a Heath
Kit HRA-10 calibrator unit.

I was originally going to use a very nice Northern Engineering 100
KHz crystal mounted in a glass octal tube enclosure. But I found that
setting the main tuning on the SX-99 is still a bit problematic at that
low a marker frequency. There's still plenty of room for error and you
end up with the dial at 7.1 or 6.9 MHz instead of 7.0 MHz.

Using a 1.000 MHz crystal, you set the band spread dial to the nearest
MHz and adjust the main tuning dial for a zero beat and you're done.
No guessing if you got it right or not.

Alltronics had a collection of LMB mini-box chassis for a very reasonable
price on eBay. $6 + $3 shipping, rather than the $15-20 + shipping I've
been seeing for the old Bud minibox chassis.

Testing things today, the 1.000 MHz crystal puts out a very nice strong
signal up to about 7 MHz where it begins to fall off rapidly. I'm going to
add a diode to the output to increase the harmonic content, hopefully
up to 30 MHz.

Yesterday I replaced the rotary SPST "Standby/Receive" with a DP3T
rotary switch. I now have "Standby/Receive/Calibrate" positions and
NO modifications or extra holes in the front panel of the SX-99.

I'd like to add that the addition of a 6SA7 penta grid converter to the
SX-99 as a product detector makes the radio a real pleasure to listen
to on CW and SSB. I did that mod about a month or so ago.



-- 
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com