I think there's been some confusion in the past about the impedance of the Sunn 81-0144 speaker that was loaded into the SB200 combo amp. The user's manual Spec page says 8 ohms, but a number of other places in the same manual say 4 ohms. And the amp is spec'd to put 200W into 4 ohms.
The other day I drove an 800 Hz sine wave into the amp and looked at the rms voltage and current at the speaker. I got readings (at various power levels) that ranged from about 9 to 11 ohms. If I had a REAL function generator, I could nail this down, but for now I'm going to state the opinion that this is an "8 ohm" speaker.
I was able to put about 86 watts into the speaker before the amp's overload light came on. With an 8 ohm dummy load, I got to 120 watts before overload, and with 4 ohm dummy load the amp pumped out about 205 watts.
As usual, if anyone has a schematic for this box, please scan and post!
Rich DM
