Ampeg manufactured the Portaflex SB-12 model amplifier from 1965-1971. This lightweight (67 pound) cabinet incorporated the flip-top design of other larger Portaflex amplifiers of the time. Although the SB-12 isn't as well known as the more powerful B-15, it is still highly sought after by musicians who use it mainly for studio recording.
The 'SB' in SB-12 stood for string bass; the '12' indicates the diameter of the speaker in inches. It contained a single-channel, 25-watt tube amplifier and a single Jensen speaker. Unlike bulk of the Portaflex line of bass amplifiers, the SB-12 was designed as a universal amplifier. It incorporated two separate inputs, one labeled "Bass" and the other "Instruments".

Ampeg SB 12 ( A true piece of music's history )