  EBEX was a long-duration balloon-borne experiment to measure the polarization
of the cosmic microwave background. The experiment had three frequency bands
centered at 150, 250, and 410 GHz and was the first to use a kilo-pixel array
of transition edge sensor (TES) bolometers aboard a balloon platform; shortly
after reaching float we operated 504, 342, and 109 TESs at each of the bands,
respectively. We describe the design and characterization of the array and the
readout system. We give the distributions of measured thermal conductances,
normal resistances, and transition temperatures. With the exception of the
thermal conductance at 150 GHz. We measured median low-loop-gain time constants
$\tau_{0}=$ 88, 46, and 57 ms and compare them to predictions. Two measurements
of bolometer absorption efficiency show high ($\sim$0.9) efficiency at 150 GHz
and medium ($\sim$0.35, and $\sim$0.25) at the two higher bands, respectively.
We measure a median total optical load of 3.6, 5.3 and 5.0 pW absorbed at the
three bands, respectively. EBEX pioneered the use of the digital version of the
frequency domain multiplexing (FDM) system which multiplexed the bias and
readout of 16 bolometers onto two wires. We present accounting of the measured
noise equivalent power. The median per-detector noise equivalent temperatures
referred to a black body with a temperature of 2.725 K are 400, 920, and 14500
$\mu$K$\sqrt{s}$ for the three bands, respectively. We compare these values to
our pre-flight predictions and to a previous balloon payload, discuss the
sources of excess noise, and the path for a future payload to make full use of
the balloon environment.
