mixed impedance cabs

[shneezy]

another stupid question, i know but any help would be awesome.
i usually run my fender 300 pro into a svt 410 hlf(4ohm) and the svt 810 ( 4 ohm) then i run my amp at two ohms ( it is switchable between 2 4 and 8)

i need the volume i am getting now for a majority of the gigs because stage volume is the only volume.

i also have a warwick 410 (8 ohms) is there anything i can do to make that cab a 4ohm cab?> so i can use only the two 410s

the guy at the local music store said i could run my amp at 4 or 8 ohms into the the 8 ohm and the 4 ohm 410. acoording to what i have learned so far that is not a good idea.
help help help!

[Bass_Pounder]

A: The question gets asked at least once a week - NO you CANNOT EVER make a 4 ohm cab an 8 ohm cab OR vice versa by simply rewiring it. You MUST change the speakers.

B: Running a 4 ohm cab with an 8 ohm cab gives you a total load of 2.67 ohms. The 4 ohm cab will get 2/3 of your power and the 8 ohm cab will getr 1/3. The guy at the local music store is an idiot (probably Altos).

[Thor]

Correct me if I am wrong but, this is a tube amp so the
output should be matched as closely as possible to the load.
The impedance switch allows you to choose which
transformer tap to use 2, 4 or 8 ohm. (This is different from a
solid state amp where the output does not need to be selected.)

The load of the circuit with the 8ohm and 4 ohm cabs is
2.67 ohms. If you use that circuit, choose the 2 ohm tap
which is closest to the actual load and you should be fine.

If you disconnect the 8 ohm cab, change the tap to 4 ohm.

Note that the 8 ohm cab will draw 1/2 less current than
the 4 ohm cab i.e the 4 will draw 2/3's of the output current
and the 8 1/3 of it.

Plug'em in and see how it sounds.

[RickenBoogie]

Like said above, it'll work, but the imbalance between the 2 cabs would be enough reason not to do it, for me.