: They require specific "current pusher" tubes with low plate resistance, such as the 6AS7, 6080, or 6336 .

: Transformers can introduce magnetic hysteresis and phase shifts that color the sound.

: Without a massive transformer to "charge up," the amplifier can respond more quickly to sudden musical peaks.

Because tubes naturally operate at high voltages and low currents—while speakers need the opposite—"tranny free" designs are complex to build:

: Common industry slang for a transformer (not to be confused with transistors).