 The transmitting tubes TT21 and TT22 have almost identical transfer characteristics to KT88 but a different pinout, and by virtue of their anode being connected to the top cap have a higher plate voltage rating (1.25 kilovolt) and a higher power output capability of 200 watts in class AB1 push–pull.The screen grid is sometimes tied to the anode so that it becomes effectively a triode with a lower maximum power output.The KT88 was introduced by GEC in 1956 as a larger variant of the KT66.