The attached link shows the sidetone for an Omni V which produces a
sine wave. I've outlined the Bridged-T oscillator in red. The older TT
rigs used the relaxation oscillator which produced a sawtooth wave. I
don't have the diagram for the Corsair but most TT rigs including
Triton, Argosy, Omni A/D, Corsair used the relaxation osc. The Delta
580, Paragon 1&2 and Omni V used this T oscillator. Q1 is likely
already in the old circuit. The ST line is your T voltage and Q1 is
simply a switch to ground the emitter of Q2 for keying the sidetone.
Pitch and Level controls are probably the same value and can remain in
the circuit.
I used the "ugly" method of construction i.e. I removed the FET
transistor and a few parts from my old Omni C, cut the foil in a few
places and haywired the parts as neatly as possible. I recommend doing
this project in one setting otherwise your train of thought will
derail. It wouldn't hurt to read up on the bridged T oscillator in the
ARRL Handbook before starting. The only critical parts are C2, C3, R4
and R5. These should be balanced in value as shown. Variations in
value will result in frequency changes.
http://members.iglou.com/n4lq/img/sidetone.htm
Steve N4LQ
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