[Amps] SGC SG-500 low output 21 mhz

[john, ke5c]

Has anyone experienced low output on 21 mhz (380 W) with normal output on 14
mhz (520 W)?  These bands use the same output filter (13.2 - 24 mhz), and
output is as expected on all other bands.  The drive is the same as for 14
mhz, and while I can't measure collector current until I get a bigger
ammeter, Vcc is the same at the amp suggesting Ic is also the same.  Thus
the problem is limited to one band which shares an output filter with
another band which is working as expected.  Thus I am wondering if a
component in the output filter has gone astray so as to change the roll-off
freqency (or if it came this way - the original owner only used it on 40
meters).  Any suggestions from any solid-state amp users/designers would be
really appreciated.  Thanks!

73, John
http://www.kkn.net/~ke5c/