Yes.
You can measure the electrical current with an amp meter. Amperage measures the current flow.
To run a monitor speaker or to connect several amps in series to pre-amp your amp.
in series to the battery from the alternator following polarity
A series circuit will produce more voltage. For example, two 12 volt automotive batteries both have a 600 amp capacity. Connect the 2 batteries in series and you will have 24 volts with 600 amp capacity. Connect the 2 batteries in parallel and you will have 12 volts with 1200 amp capacity.
If your amp meter is showing 208 volts but you need 240 volts, you may need to check the connection or source supplying the power. Ensure that the voltage source can deliver 240 volts and that there are no issues with the wiring or circuit. Consider consulting with a qualified electrician to address the discrepancy and ensure safe operation.
yes, it is 12 volts
you get a transformer...
If your amp has a "line out" jack (most likely on the back of amp), you can run a patch cord from the line out jack to an input jack on your mixing board. An earphone jack will work also, but not quite as well, as that is not what it was specifically designed for.
Volts x Amps = Watts On 120 V you can connect 1200 W...although you might want to leave some room.
If you have the right test equipment amps are the easiest to measure. A slip over the wire amp meter is easier to use than a clamp on amp meter. The other two values have to be measured by using test leads from the test equipment.
a meter for amps
The voltage will increase but the amperage will stay the same. For instance: Connect 2 12 volt 100 amp batteries in series and you will have 24 volts at 100 amps.