SB-401

[Dick Blaney]

Hi gang,
I gotta problem.  It's got me stumped.  My SB-401 works great, except for
the tune and CW positions of the function switch.  When in either tune or
CW, the "Mic/CW level" pot will not control the carrier level.  When in SSB,
the mic gain is controlled by it's pot.  I know that these are 2 different
pots ganged together on one shaft, and it is only R-16, (the one that
controls the carrier), that is misbehaving.  I've checked voltages,
resistances, caps, values, grounds, etc., and have found nothing out of
place.  Voltage at the wiper of R-16 appears to act normal, as does the
voltage that it feeds to the corner of the balanced modulator to unbalance
it.  The plate current is high, (and RF output is high),  with R-16 at
minimum, (CCW), and with it at maximum, (CW), but decreases when it is about
the middle of it's range, then rises again turning it further.  Anyone had
anything like this invade their " '401 poor man's Collins"?   I'm about to
pull whats left of this gray mop out by the roots.  It's got me almost
whipped.  Any suggestions?  I would appreciate any help from  anyone that
has seen this before.  Thanks in advance.
73 de
Dick, WB8MHE
wb8mhe at bright.net

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