Constant sidetone

[Mark Graalman WB8JKR]

  I've come up with an idea that MIGHT do away with
the constant sidetone in the HW101 when the rig is in
the CW mode but the key up. Let me preface this by
saying that placing a .01 uf cap from the below indicated
point (C315/R329 junction) will stop the constant tone

  On the schematic the output of V15A is coupled to V15B
through C315 and R329, the reason the sidetone is always
heard is because the inter-electrode "C" of V15B couples
it to the audio amp V14B no amount of cutoff bias to V15B
will cure the problem. Here's my idea:

 Place another .005 disk cap in series with C315 then at the
junction of these two caps connect a diode with the anode to
chassis ground, then connect one end of a 22K resistor from
the junction of the two capacitors and the diode cathode to the
CW key jack. When the key is up the diode will be biased "on"
by the -55 volts at the key terminal thus bypassing the audio
tone from V15A to ground. When the key is pressed the bias
is removed from the diode and the audio is allowed to the grid
of V15B. The 22K resistor allows the key line voltage to bias
the diode on without placing the rig into the transmit mode.

  Any thoughts? Criticisms?


  73, Mark WB8JKR

Novice 3/71, General 8/72, Advanced 6/80, Extra 8/88
Member Society of Cable Telecommunication Engineers
Member ARRL, DXCC, WAC, WAS, VUCC 2 meters, GJDXCC, OTC, RCC, QCWA

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