The Western Electric 300B contains a directly heated, oxide-coated filament. Though this combination is by no means unique to the 300B, the filament coating is. A strontium and barium mix is combined with other proprietary constituents in the ribbon to form a coating that was originally developed for use in underwater sea cable applications and later adopted for use in the 300B’s cathode. It’s often refer to it as the secret-sauce or secret formula. This special coating not only improves the lifetime of each tube, but also powerfully enables the dynamics required for great music reproduction. As a signal is propagated through a 300B, the filament remains “hot,” never fully depleted of electrons, always at the ready. When we experience the pleasurable, water-clear sound of a 300B, we’re experiencing the thermal inertia of a directly heated cathode. Check the video below…
In the video you can see Western Electric’s electron tube staff prepare and apply the special filament coating that makes our famous triode truly unique.