Controlled r.f. power generation using magnetically-beamed triodes

The magnetically-beamed triode has a structure radically different from a conventional industrial triode. The relatively small proportion of the current which is intercepted by the control electrode (gate), even when it is driven to a high positive potential, leads to useful design properties and novel applications circuits. The cool gate needs no special coating to inhibit electron emission and oxide-coated cathodes are used to complete a robust structure and reduce ancillary heater power. Low gate current results in low bias loss and low oscillator drive power. The latter permits the introduction of a new form of oscillator output power control by limiting the gate voltage swing by a catching-diode in conjunction with a solid-state regulator. Design parameters are considered for this unit which is less costly than alternative systems. Oscillator power may be controlled from maximum down to 10% by the swing of only a few volts at the regulator input. Provision may be made for external feedback loops in addition to a manual presetting potentiometer. Examples are quoted for the stabilization of input current or r.f. output voltage.