AMC 2100as bias help

I own an AMC 2100a tube amp.I wondering what would be the SAFEST way to bias it. I really don't like the idea of having to connect to the resistors inside. I would much rather monitor the output and try to fix it there. My left channel is just slightly more reserved than the right which is a bit brighter. I would also like to know if there are any affordable oscilloscopes out there that anyone would recommend. I may post more questions later but for now this is what I need to know.