Originally posted by jsthvfn2000If you have a tube amp you must adjust the output transformer to match the load. They don't have a setting for a 12-Ohm load.
...So, I could run both cabs in series but the 8 ohm cab will not be as loud as the 4 ohm cab. Will doing this hurt my amp?...
A transistor amp is OK with just about any load that is greater than the rated minimum.
In a series circuit, the current is the same all the way through, but the voltage will divide up in proportion to the impedance. Since Power = Voltage x Current, the 8-Ohm cab will get twice as much of the power as the 4-Ohm cab.
Whether it sounds any louder depends on how efficient it is, compared to the other cab. Most people can't distinguish a difference that is smaller than 3 dB - that means you have to double (or half) the power before it becomes noticeable.