http://elecraft.85.s1.nabble.com/K3-keying-an-amplifier-tp6033183p6033485.html
I don't think the diode isolation will work in this case.
>> You might have a problem when only one rig is powered up, with the
>> unpowered one pulling down the key/control line. The K3 is OK, as both
>> outputs are open drain/collector. If that's also the case with the ICOM,
>> the "Y" connector should work. If the ICOM has a pull-up resistor, or
>> anything except an open drain/collector connected to that control line,
>> there could be a problem...
>
> In that case, a Schottky steering diode can be used on the Icom key line. A
> 1N914 or 1N400X series may be fine but I've seen instances where the higher
> diode junction voltage prevents the line from going low enough to circuit
> ground potential. Not sure how sensitive the Alpha 9500 is to that effect.
> I agree with Scott that the K3 should be fine with its open-drain on the
> MOSFET switch.
>
> I don't see this issue very often on the amp key line -- I do see it often
> when trying to use a single CW keyer, feeding multiple transceiver's in
> parallel, due to the use of pull-up resistors on the paddle key line.
> Again, Schottky steering diodes used for isolation at the input to each
> transceiver's CW key line solves the problem.
>
> Paul, W9AC
>
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