[R-390] What is the Crystal in the 51J filter ?

[John Kolb]

On Mon, 21 Jan 2002, Rodney Bunt wrote:

> I am restoring a 51J the crystal filter section is missing, so I am
rebuilding it, I can make up a
> switch, and even a differential capacitor. So, what is special (if
anything) about the 500KHz
> crystal.

I don't know what crystal was used in the 51J xtal filter, but the
usual 455 kHz xtal filter xtal was a small black plastic case with
solder lug terminals coming off both sides, for lower shunt capacity
across the filter than the FT-243 or other holders of that period.
I would expect an HC-6 holder xtal would work well, the version with
long wire leads even better. Bend the leads at right angles as
soon as they leave the case for lower stray C. Wire up the xtal
filter with heavy stiff wire, running straight from point A to
point B, rather than looped in a circular path for stability.
At the same time, the circuit should be arranged to have as little
stray C as possible.

John