Guitar Amp Repair

[morbe]

Hello everyone new to the Forum and very Stupid when it comes to electronics. So I have a few questions to ask. I play the guitar and sing in a band. For starters let me say that the only thing I know about Electricity is that the outlet goes into the receptacle, LOL that's just about it.
Any how I was setting up my equipment and did a sound check with guitar and mic. I felt a static discharge like shock when I placed my lips on the mic, I dismissed it as static discharge but When I placed my lips on the mic again I got a shock. Not a massive shock but a discharge type shock.
I then noticed that the PA was plugged into a power strip that looked as if it had a few arcs burns in between each outlet. Then this power strip was plugged into another power strip that didnt look any better. I only got shocked when I held my guitar strings and kissed the mic. I then demanded the PA be plugged into a different outlet. and I was able to complete the practice session with out further incidents.

So here are my questions.

What caused this? Does daisy chaining power strips cause this? I tested the outlets with outlet testers and no cross polarity and the ground was present in the wall socket. I didn't get to check the power strips.

Was it a Ground issue? I checked my Amp and PA to make sure that the Ground Prongs had continuity with the Chassis. My elementary level of electrics told me that there was no ground lift on either Amp nor PA right?

Finally. could it be my amp? I had my amp for at least a year now and now issues. My amp is a newer amp with a 3 prong plug but its not the original plug. It looks as if the the original cord was damaged and they cut the original prongs off and replaced the plug head with one of these,
**broken link removed**
My main question is could this have been hooked up backward creating cross polarity in my amp? I'm assuming if it was I would have had a way more severe shock that could have been lethal.

 

[unclejed613]

check your amp for a "polarity" switch on the back. if there isn't one there, try turning the 2 prong plug 180 degrees in the outlet. before the days when 3-wire plugs became common for guitar amplifiers (hot, neutral, and ground), there were circuits using a resistor and capacitor from what was supposed to be the neutral of a 2 wire power cord to the amp chassis. when 2 amplifiers using this arrangement are plugged in with one plug reversed, there's a 60-120V difference between the two "grounds". because the resistor was something like 470k and the cap was 0.01uf, the resulting current when you get between these two "grounds" (by touching the guitar strings, which are connected to the chassis of one amp, and then touching the mic case, which is connected to the chassis of the other amp) was usually pretty small. best bet is to replace the power cords with 3-wire cords, so you have real grounds for the chassis, and isolate the "neutrals" in the amps from the chassis (remove the RC network). the "polarity" switch on many amps just switched the RC network between hot and neutral. when i was in a band, i would spend about 10 minutes cross-checking amp grounds with an AC volt meter to make sure everybody's amp was not going to be a shock hazard.