The Hughes & Kettner "BATT" tube bass preamp, discontinued in the mid-90s, is an all-tube, half-rack preamp/amplifier. Its five-watt power amplifier will drive a speaker to practice levels.
Of particular note is the ability to take a line- or instrument-level signal from either the preamp or the power amp stages. Taking the signal from the power amp provides all of the output-transformer coloration that a tube amp has. I've used it as a preamp in a live-performance rack to good effect, and also to re-amp a bass track in the studio.
The BATT manual.. I've added a block diagram; the manual never had one, though there is one silk-screened atop the unit.