c. Later in this lesson, you will learn exactly how a magnetron meets
these three oscillator requirements of a tuned circuit, tuned circuit
excitation, and regeneration.
10. How a magnetron works.
You know from examining the construction of a magnetron that it
consists of a diode and permanent magnet. If we combine the qualities of a
permanent magnet with the operation of a diode, you will get a good idea of
how a magnetron works. We will start with the operation of a diode, next
the magnet, and then put the two together.
11. Electron flow in diode tube.
a. You know that a diode tube has two main elements: the cathode and
the anode (plate). The cathode is coated with a chemical substance such as
thorium oxide, which emits electrons when heated. Electrons flow from the
hot cathode to the anode only when the anode is at positive potential with
respect to the cathode.
The circuit action for ordinary diodes and
magnetron diodes is the same, but the circuit arrangement is slightly
different. The two arrangements are compared below.
(1) In ordinary diode tube circuits, the cathode is connected to
negative voltage and is grounded.
The anode is then connected to the
positive terminal of the same DC source.
(2) In magnetron diode circuits, the cathode is still connected to
negative voltage and the plate to positive voltage, but the plate is
grounded instead of the cathode.
b. The diode circuit action, of course, is still exactly the same.
Electrons flow from the heated cathode to the positive plate. Grounding the
plate instead of the cathode does not affect the diode circuit action.
c. The magnetron anode actually forms the metal envelope of the tube.
So, when the magnetron is bolted to a radar chassis, the anode becomes
grounded. Electrons flow when the high voltage DC pulse is applied to the
cathode (Figure 87). Grounding the anode this way prevents a shock hazard
when the high-voltage pulse is applied to the magnetron.