This is not a good environment to be venturing into without a healthy fear of the death risk you're facing inside this amp. What happened when you left the cover off and fired it up:
There is what is called "shorting bar", or "safety interlock" in your 2200 (nice amp btw). This was shorted to ground. This protected you from death, but it also probably damaged the plate circuit. It can destroy the plate transformer,'glitch' resistor, one or more diodes in the brige/doubler bank, the filter caps, and/or all other components in the HV supply.
I suggest you try to find an "elmer" close by to help you check the plate transformer, troubleshoot the metering board and the HV filter caps --- Because one, or a combination of those have definitely sacrificed themselves as they were designed to do.
I cannot stress enough, the risk of death here though. It requires the right tools and skills to proceed further.