[Collins] KWS-1 Crystal problem

[Dr. Gerald N. Johnson, electrical engineer]

Sounds about normal for JAN crystals. A significant portion of the
crystals I've bought from them have arrived not working. Generally their
second try worked. I've had much better results (at a distinctly higher
cost) from International Crystal.

The low oscillator gain in the KWS-1 could be a weak tube, open cathode
bypass capacitor, changed cathode resistor value reducing plate current,
leaky screen bypass lowering screen voltage and cooking the screen
resistor to a higher value while reducing the plate current. Reduced
plate current generally means reduced stage gain. Could be a leaky
(though less likely) mica capacitor in the grid circuit. Could be that
the paper screen bypass needs to have a .001 disk in parallel with it to
get the screen truly bypassed at higher frequencies. I don't have a
schematic for the KWS-1 handy so I can't be more specific. Could be that
the mica capacitor in the plate circuit is leaky. Could be that the coil
form has accumulated moisture enough in the past 40 years to become
lossy. Could be a combination of a bit of all the above.

Radios of that age generally have leaky molded paper capacitors, and
carbon composition resistors that have drifted in value significant
amounts. A long time ago, I saw a resistor doubled in value in a vintage
TV set, made the horizontal lock at half frequency with a sync bar down
the middle of the picture on the round metal picture tube. Because the
low frequency also reduced the high voltage, it looked like it was
synching at the wrong place, but there really were two pictures side by
side. The resistors in the KWS-1 started out life with higher quality,
but have had more decades to age than that TV set did.

73, Jerry, K0CQ
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Entire content copyright Dr. Gerald N. Johnson. Reproduction by
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