What about old heavy 120VAC equipment. Drake, Kenwood, Collins etc?
What did portable stations do back in the 50's-60's?
We didn't have modified sine wave generators in the 50's-60's.
They were gas motors driving an alternator, with a speed
regulator to set the frequency, so most ran at 3600 RPM.
(If you were really flush you might have an Onan that ran at
1800 RPM, and seemed much quieter.) Electric clocks were
pretty unreliable, although the sweep second hand could be
compared to a wrist watch and used to set the regulator.
Even now, most of our equipment on a club Field Day runs from
AC power supplies plugged into a generator, including linear ones
with a transformer. It has been a few years since I've seen a
TR-4C, KWM-2, NC-300, or Heathkit Apache plugged in at Field
Day, but I haven't seen any issues so far.
Well, except when the generators didn't receive proper maintenance,
or generated too much RF noise. One year we started several hours
late, finally on the 4th generator we tried.
That's not to say there might not be an issue with modified sine waves,
but I haven't experienced it yet (other than possible RF noise).