Three things you need to know...
1) is there an internal ground connection to the mains safety ground input?
2) is there any high voltage on the outside parts?
3) is there any dc offset on the output?
1) is there an internal ground connection to the mains safety ground input?
Disconnect from the mains.
Wait 2 hours.
Remove the cover (presumably the bottom).
Look inside.
If in doubt take clear photographs and post here.
2) is there any high voltage on outside parts?
Answer question 1 first and assure yourself that all is safe.
Safely reattach cover.
Turn off on amp.
Turn off mains socket switch.
Ready fire extinguisher.
Plug mains cable into amp and then into mains.
Turn on amp at amp.
Stand back.
Turn on amp at mains. Cover mains switch. If any 'unusual noise' or smoke turn off mains switch immediately and disconnect lead from mains socket.
If all appears normal...
Use meter to check metal parts on outside of chassis for high voltage. First check meter is working. If working then set meter to high voltage range suitable for the amp under test. Attach one meter probe (conventionally the black) to mains ground. Use the other probe to probe the external metal parts. Do this one handedly. Keep the second hand behind your back (in this way fault current can not pass up your arm, across your chest and through your heart on it's way to ground via your other arm).
If there is voltage on external parts turn off mains socket switch immediately, disconnect from mains socket, and leave for two hours.
3) is there any dc offset on the output?
You are going to need a spare jack plug or an old set of 'phones that you don't mind putting at risk...
But do items 1 and 2 first, then we can discuss item 3.
: )
