Good troubleshooting can and should be done with this type of equipment de-energized. Experienced people know how to do this. It works most of the time. If there's a good reason to have the equipment running one can use a cell phone camera to look for zorching. There should be a sticky listing safety rules for over 50 volts here. Maybe there is and I haven't seen it.
Hi Dave, Jen and I really enjoyed the visit with you and your wife. Thanks for stopping by and liberating the amp from my Round Tuit closet! 73