Amen to the caution about working on gear when tired or perhaps otherwise impaired. Best to go at things with a fresh, alert mind, and with care.
A long time ago a friend of mine sustained serious injury when he brushed a couple of terminals in the power supply of a mighty tube amp he had just built. He was tweaking the bias and balance controls underchassis when his pinkie finger on his right hand went some place in the chassis where no pinkie should go. He burned two craters clean to the bone in that finger, and his whole arm turned black-and-blue, and was numb and paralyzed for several minutes. He said he felt like he was trampled in a stampede, and his arm tingled and buzzed for several hours after the incident. He was tempted to get himself to hospital, but wasn't sure he could drive safely, and nobody else was home at the time.
The power transformer was a mil-spec type with a series of windings wired up and rectified to produce a 900V potential at 1 ampere. It was the terminals of the 1000mf main filter he brushed.
He laid out the following rules after that:
1) No working on such gear when impaired by fatigue or imbibement.
2) Try to have an assistant on hand (usually me) if undertaking a hazardous task with powerful equipment.
3) Always be sure that one can get help if things go bad.
4) Never place both hands in the chassis unless the power is down and the 'lytics are double and triple-checked for charge.
My good friend is still around to tell the tale, because his left hand happened not to be on the bench at the time, and the lion's share of the current went through 2 inches of finger. If it had gone through his torso from hand to hand God only knows....
