[Elecraft] SB-221 for K3 need some help.

[Don Rasmussen]

Tom - I have the soft key, but thought I didn't need
it after seeing the K3 specs. Why would you depart
from that measurement? ;-)

The T-R output MOSFET in the K3 is rated at 200VDC at
around 5A, so it
should not be much of a concern for switching.
Additionally, the MOSFET
is diode-protected against reverse spikes from the
relay it's keying.

HOWEVER... this having been said, were it me, I'd add
an (internal)
Lo-voltage keying interface, like that offered by
Harbach, to change
the T-R keying voltage presented by the SB-221 from
120VDC to around
2VDC and maybe a couple mA of current. Pretty
economical and easy to
install, and worth the effort to install.