In this case, each cabinet requires an AC outlet. That leaves one for a wireless unit or something else.
The self powered power amp cabs were ahead of their time but not unique. Leslie organ speaker cabinet were power amps as well and pre-dated what Ampeg did.
Fender’s wireless unit. James Jamerson was photographed using one.
Introduced in 1961.
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I had the Gibson Les Paul bass amp.
Similar deal- a small solid-state head that provided some initial gain and EQ, and fed a 200 watt power amp that was stuffed in the bottom of the matching twin-15 cab.
I bought it on impulse in the early '70's, after seeing it up in the roof at the Canadian Norlin warehouse. I used to go up on this catwalk to look at all the B-stock stuff, like LP Juniors with minor finish blems. They typically went for about $80, IRRC.
Anyway, I had seen the ads in Guitar Player for the Les Paul guitar stack, with this huge, compound-driver cab. It had 10's, 12's and whatever else they could find to stuff in there, and it looked pretty majestic. I never saw or heard one out in the wild, so I have no idea what they sounded like. However, they looked pretty majestic.
Anyway, I had just finished my first and only recording project with my dad, and had $225 burning a hole in my pocket. The amp was sitting up there looking lonely and the price was right, so I grabbed it and ran.
Just like the guitar version, the bass stack had a lot of visual presence. Little pea-bulbs behind an acrylic front plate, so each section of the control panel was colour-coded. The cab had blue-ish grille cloth with tinsel woven into it, which looked pretty surreal under stage lighting. It didn't hurt that it was absurdly large for a 2x15, even accounting for the fact that it was intended for bass. It was loaded with square-magnet Emminence drivers, the first I ever saw.
Sadly, the experience on stage was pretty anticlimactic. It was punishingly loud by the standards of the day, but even with a Fender bass with the tone control wide open, it had almost no upper mids or treble. Just a big, pillowy rumble, like a whale calling it's mate from under water. Even when I pushed it into distortion, there was simply no definition to be had.
I can't even imagine what it would have sounded like if you paired it with an EBO with a mudbucker at the neck...