[Amps] SB221 Low Power Help

[Rahul Sathe]

Hello Experts,

My name is Rahul call VU3RAZ. This is my first post to the list. I am
seeking help on fixing my old SB221.

as such the amp works on all bands, no arc or parastatics, tuning and
loading is smooth and easy.. I am not able to load the amp to full rated
plate current even with a 100 W drive with my 756 Pro3. Input VSWR is high,
I tried tuning the input tuned circuit but no luck on few bands (20, 15).
With the 756 ATU the things improve but I can not get plate current beyond ~
400 mA. Even tried disconnecting HT from each tube to see if one if the
3-500 is dead... both work but even with single tube I am not able to load
the amp fully. Am I looking at dead (weak) tubes ... can both of them show
exact same behavior? Or I am missing something I am not sure if I need to re
build the  PSU (replace caps)

Please help...

73
DE VU3RAZ