The 45Z3 is a medium-mu double triode tube, often used in Hartley oscillators and in some radio-controlled devices. It was introduced by RCA in the 1950s and is part of the 45 family of medium-mu tubes. It is similar to the 45, except that the triodes are arranged in a stacked configuration for higher gain.
The 45Z3 has a high transconductance of about 6.3mA/V, an amplification factor of 20.9, a maximum anode voltage of 125V, and a maximum anode dissipation of 3.5W. It is well suited for high gain applications, such as voltage-controlled amplifiers, cathode followers, transconductance amplifiers, and multi-loop feedback amplifiers. It is also used in low-level audio and IF stages, where its wide frequency range of 25Hz to 700kHz makes it suitable for stereo applications.