A new audio output valve, the KT88, with an anode dissipation of 35 Watts has been introduced by The General Electric Co. Ltd. This valve is a higher-power version of the familiar KT66, although it is smaller in size. It does not replace the KT66, but is complementary to it for output powers in excess of those readily available from existing KT66 circuits.
An example of the usefulness of this new valve for public address equipment is that, at a supply voltage of 500V, with auto-bias operation, the available power output is 50W or twice that obtainable from a pair of types KT66. At a supply voltage of 560V, with fixed bias operation, output power of 100W is available.
The KT88 has a larger cathode, allowing for a higher mutual conductance, and a more modern type of construction permitting the use of higher anode voltages and dissipations. It. is designed for use mainly in a push-pull circuit and will operate satisfactorily as either a triode or a pentode. In the ultra-linear (UL) circuit, satisfactory operation is obtained with the screen grids connected to tapping points including from 20%, to 40% of the total turns of each half-primary.