  It was recently discovered that the amplitudes of pulsating red giants and
supergiants vary significantly on time scales of 20-30 pulsation periods. Here,
we analyze the amplitude variability in 29 pulsating yellow supergiants (5 RVa,
4 RVb, 9 SRd, 7 long-period Cepheid, and 4 yellow hypergiant stars), using
visual observations from the AAVSO International Database, and Fourier and
wavelet analysis using the AAVSO's VSTAR package. We find that these stars vary
in amplitude by factors of up to 10 or more (but more typically 3-5), on a mean
time scale (L) of 33 +/- 4 pulsation periods (P). Each of the five sub-types
shows this same behavior, which is very similar to that of the pulsating red
giants, for which the median L/P was 31. For the RVb stars, the lengths of the
cycles of amplitude variability are the same as the long secondary periods, to
within the uncertainty of each.
