Help? SB-101 keeps tripping into XMIT

[Ed Lambert" "K1ZOK]

The good news is that's there's not too much circuitry to investigate.
The problem is that the relay driver V12B is tripping back on after you
release the PTT.  When the PTT is released, that should make the cathode
of the tube go back to +15 volts which should turn it off.  The positive
voltage is fed through R219 and is controlled by the zener diode D202.
This is the first check point.

The grid of V12B is fed with rectified audio from the VOX amp.  This
voltage charges C213 to allow for short pauses in audio and prevents
quick turn off.  The VOX delay control and R903 are used to discharge
C213 and determine the length of time of the delay.  If either or the
resistors are open or have increased in value (common problem) the
voltage will remain on the grid and the tube can conduct even though the
cathode has gone to +15.

And a tube that gets gassy can also cause it to conduct.  Exchange V12
and V1 to eliminate that possibility.

Ed
K1ZOK

On Sat, 14 Apr 2001 11:25:59 -0400 Zeiger-Guerra Family <zgfam at P3.NET>
writes:
> Newly acquired SB-101 is a great receiver.  Once rig has warmed up
> and I
> begin transmitting (PTT) I only hear 1 or 2 seconds of audio after
> releasing
> PTT and the rig trips back into XMIT.

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