You should have the original amp updated to a three wire line cord. Most techs will remove the death cap when they do this. If you just remove the death cap but leave the two wire cord, the amp will always shock you and it could kill your effects pedals anytime it's plugged in. It doesn't even have to be turned on.
To protect pedals, always plug a cable into the amp (or guitar) first, then into the effect. Or, unplug the amp before connecting the effects. This will be a problem if you want to change guitars between songs. When using a two wire amp you could kill the effect when changing guitars and not be able to make a sound when the song starts.
PA systems can be a problem if they are not properly grounded with a three wire line cord. If it's not, it will cause nothing but problems, get it fixed. If the PA is properly grounded and you are using a two wire amp, touch the microphone with some metal part of one of the tuning pegs or a string on your guitar after it's plugged into your amp and the amp is on. If you see a spark, reverse the polarity switch on your amp and try again. If you can't eliminate the spark, unplug the amp and don't use it until it's fixed.