[Heathkit] no power output

[Vicki Brunetti]

my sb221 quit working,voltage looks good,it tunes and loads ok but it
only puts out about 100 watts with 50 watts in. with grid @ 150 ma,plate
abt .6 ma,as power is added the plate goes to .9 ma and the tubes begin
to glow deep red.ive tried new tubes with the same result the zenor
checks ok,plate choke looks clean, everything looks good , but im just
guessing here.can anyone help? ...n4aze