  The Bloch-oscillating transistor (BOT) is an amplifier that utilizes
semiclassical dynamics of states in energy bands under traveling quasimomentum.
In a BOT, a single quasiparticle tunneling across a base tunnel junction
switches the state of a superconducting tunnel junction to a lower Bloch band,
triggering a series of resonant Cooper-pair tunnelings through an emitter
Josephson junction (Bloch oscillations). Here, we investigate experimentally
and theoretically an alternative realization of this device, based only on
superconducting tunnel junctions. We discover new amplification schemes, where
the periodic motion of the quasimomentum is used to control charge transport
between the electrodes. Remarkable, in operation the resonant Cooper-pair
transport across the base Josephson junction occurs repeatedly to two opposite
directions.
