Dx-60 sidetone

[wa1vwl]

Boy this DX-60 sidetone thread has generated a lot of responses. I have
a couple of ideas I'd like to add. First, why not "borrow" the HW-16
sidetone circuit? The HW-16 uses grid block keying like the DX-60. It's
pretty simple but effective. Of course, the sound of a neon relaxation
oscillator is not the most pleasant thing to hear but it's better than
nothing. Looks like am NE-2 with a .002uF in parallel. One end of the
combination is connected to B+ (310 Volts) with a 1.5 mOhm resistor. The
other end of the combination is connected to the keying line. The
oscillator is coupled to an audio stage in the receiving section at the
1.5 mOhm side through a 390 pF and 470 kOhm series combination. In the
late 70's I used to have an HW-16 and replaced the sidetone circuit with
idea number two: "borrow" the Drake 2-NT circuit. That one is a little
more involved but much better-sounding. It consists of a phase shift
oscillator and was described in CQ, October 1969 on page 52. Briefly, on
key up there is a diode switch which adds a large capacitor to the phase
shifting circuit to stop oscillation. With key down, the diode is
grounded and does not conduct thus enabling oscillation. The output is a
pure sine wave. A long time ago, I also adapted this diode switching
idea to a tube oscillator circuit and obtained similarly good results.

73/Gerry/W1ID

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