[TenTec] ARGONAUT 509 SIDETONE CHIRP

[Ed Worst]

Hello once again.  A while back I asked about an instability in the sidetone
of my Argonaut 509.  I got several very good responses, but no one actually
claimed victory over this problem.  In fact I found that there were several
others who had the same problem and wanted to be notified if I ever managed
to fix it.

Well, I'm here to claim victory.  After applying DeOxit on the sidetone
Volume and Tone control pots and doing the same with the Audio Board
connector pins - without any noticeable improvement - it was time to melt
solder.  I re-soldered all the connections on the bottom of the Audio Board
in hopes of repairing a cold solder connection or hairline fracture, but
still no improvement.  Then I replaced Q3 on the Audio Board, and that did
it.  Q3 switches C5, a 0.1mfd capacitor to ground which activates the
unijunction
transistor relaxation oscillator.  If Q3 isn't saturating or its On
resistance isn't steady, it will affect the frequency of the sidetone.  It's
been working great for over a week now without a single "chirp".

I don't know if this is the fix for ALL sidetone stability problems, but it
certainly fixed mine.  Hope this is of some help for others with chirpy
sidetones.

72/73,
ed - k9ew