So this is an old story. Or rather an old trick that I dont hear too much about. I have an old Traynor tube combo that I play my synthesizers through. It's a 2x12 guitar combo, goes by the name of YGL3. I recently moved all my music equipment to a new space, and on firing up the amp it sounded kind of off. I peeked at the tubes and one of them was off. Not funny off, OFF off. So I did the normal thing. I pulled half the power tubes and plugged it into a an 8 ohm cabinet (the previous speaker impedance was 4 ohms). The only trepidation I have about this, is that in my experience, Traynor amps brutalize EL34 tubes pretty good. Some sources I have read on the interwebs claim that half tubing is fine, but you have shortened tube life. Conflicting sources claim it makes no difference as long as you double the impedance.