The KT90, or in full, "Kinkless Tetrode 90", is a beam power tetrode and features the same octal socket as its smaller variant, the KT88. It may therefore be used as a substitute, given appropriate re-biasing when used in push-pull configuration.[1]
The KT90 is currently manufactured by Electro-Harmonix, who claim that, despite its different construction, it possesses similar sound characteristics to the EL34 valve.[2] Semi-formal research has been conducted by U.K. supplier Watford Valves who have published a test report.[3] (This research is described here as "semi-formal" because it consists primarily of listening evaluations which may be subjective, rather than electrical analyses of performance parameters in either numerical or graphical form.)
