[Amps] SB220 running plate current when no drive

[Steve AA7V]

Hello to the group;

My SB220 has started to act up.

Immediately upon power on, the 3-500s both start drawing plate current. The
meter shows approximately 250 ma of current. It is apparent some component
has failed.

Also, it appears the grid current meter is showing a negative value (if
this is possible) as the needle now rests on the left peg.

I am not adverse to troubleshooting to the component level but would
appreciate any advice as to how to narrow my search to a specific set of
probable causes.

If I am unable to fix this amp, does anyone have any recommendations
towards a person that works on SB220s?

Regards

Steve AA7V