[Elecraft] KPA500 Mosfet SD2933 vs VRF2933

[Michael Carter]

Hi Ziv,

The SD2933 is an older part - Mouser lists it as 'obsolete'
and otherwise unavailable.  A review of the datasheets
for the two devices (VRF2933, SD2933) reveals that the
VRF2933 has a higher drain-source breakdown voltage
than the SD2933, and it is tolerant of SWR values up
to 70:1.  The SD2933 tolerates at least SWR of 3:1, possibly
greater, but that is the only spec in its datasheet.  The
VRF2933 has a somewhat lower gate capacitance than the
SD2933.  In other respects, the two MOSFETs are very similar.

I suspect the SD2933 will work in place of the VRF2933, but
you may need to watch the SWR on your antennas a bit more
carefully to avoid exceeding the maximum drain-source
breakdown voltage.  You will also need to carefully check
and adjust the gate bias voltage pots to ensure the proper
quiescent drain currents in each MOSFET.

73,
Mike, K8CN