1 duojet55 4 years ago This is my circa 1966 6170 Pro Bass amp. It puts it's tube-powered 35 watts through a 15" speaker. There were three instrument inputs, a volume, bass and treble control and an on/off/on line reverse switch on the front. The toggle switch protruded inconveniently (AND unprotectedly) on these earlier models. Later versions of the Pro Bass had two rocker switches in place of the toggle, an on/off and a separate line reverse. It isn't a bad practice amp for bass, but lacks real low-end. A lot of guitarists actually use these amps for their six-strings.