Class C operation seems very well suited to HF CW operation. At least
if the resulting envelope looks "nice" by ARRL handbook definition of
keyclick reduction, I guess.

But is it good enough for RTTY?

How about for PSK-31? Olivia?

What I've got is an old Eico 720 (Novice 75W-class transmitter biased
for deep class C, for those too young to remember) that I currently
use for CW, but would like to try out for RTTY or maybe PSK-31 by
feeding appropriate waveforms into the "VFO in" jack. My gut feeling
is that RTTY would be OK but don't really understand how class C will
mess up the PSK-31 waveform or introduce intermod that will make the
resulting spectrum broader than necessary.

The Class C stages will clearly fail the usual SSB two-tone testing
but what is a more appropriate test to say that it's good enough - or
not - for PSK-31?

Tim N3QE