Meant to power additional speakers for larger venues this amp would be fed a
line level from another amp or mixing board, hence the term slave. It was essentially
a four EL34 powered BTO sans pre-amp.
This particular example of the BTO Slave has had a pre-amp section added for
use as a bass amplifier. The four silver tipped knobs on the left are custom.
A stock Slave would have only the large center "Gain" control.
Amp courtesy H. McTavish