What is Dynatron Oscillator : Working and Its Applications

Oscillators are used to generate continues waveforms without applying any input. And there are many types in oscillator circuits. In that dynatron oscillator is one of the oscillators which shows a negative resistance characteristic. This oscillator doesn’t use the feedback system to generate oscillations in which all the remaining oscillators are using the technique. At the end of this article, you can have an idea about the dynatron oscillator definition, oscillator circuit diagram, oscillator design, and its applications.

What is Dynatron Oscillator?

It is invented by Albert Hull in the year of 1918. Dynatron oscillator can be defined as “it is a vacuum tube electronic circuit which produces continuous waveforms without applying any input”. It has negative resistance characteristics due to the secondary emission process in the vacuum tube.

Dynatron Oscillator Circuit

The below diagram shows the dynatron oscillator circuit. This oscillator includes a tetrode. Here tetrode is a vacuum tube that includes four active electrodes such as thermionic cathode, two grids, and a plate. In some tetrodes, the plate has differential resistance behavior. Because the electrons hit the out of the plate when they are coming from the cathode which is known as secondary emission. And this is the reason for the oscillator showing the negative resistance characteristics.


Coming to the dynatron oscillator design, a vacuum tube is used in this oscillator circuit which uses a tetrode. And an LC circuit (tuned circuit) connected between electrode and cathode of the oscillator circuit to store the electrical energy in the form of oscillations current. Here, the tetrode shows the negative resistance characteristics like when the voltage on the electrode increases the output current is going to be decreased for a particular range of voltages. This is called the negative resistance region of the oscillator.

“Here, the tuned circuit is connected between the electrode and cathode of this oscillator. The negative resistance effect of the tetrode tube cancels the positive resistance of the tuned circuit. Therefore the tuned circuit will have zero resistance. So, the oscillating voltage at the resonant frequency will be generated. The required oscillating voltage can be achieved by choosing the required inductor and capacitor value on the tuned circuit”. The advantage of using the LC circuit to the oscillator is, it can be operated in a wide range of frequencies. The oscillation frequency of the this oscillator is

1/2π √1/LC –(R/2L + 1/2Cr)2


The above equation shows the resonance frequency of the oscillator and in those R, L and C are the resistors, Inductor and capacitor value and r is the numerical value of the negative resistance.

Dynatron Oscillator Output Characteristics

The below graph shows the sample o/p characteristics of the oscillator. It has negative resistance characteristics so when the electrode voltage increases the output current decreases for a particular range of voltage level. Then after it can act like a normal amplifier and a detector.



The applications of the dynatron  oscillator are discussed below. They are:

  • It is used as an amplifier.
  • As a detector also it is used.
  • To measure the tuned circuit resistance.
  • Used to convert certain receivers into receivers of a continuous wave code.
  • Also applicable in converting a broadcast receiver.
  • Used as a substitute oscillator in superheterodyne receivers.

Dynatron oscillator is a widely used oscillator in receiver circuits and alternative tuned circuits in the superheterodyne receiver because of its wide operating frequency range. In the Second World War, these were used in many applications. And now these are preferred by its negative resistance characteristics in radio receivers. And till now we observed the output characteristics and circuit analysis of the oscillator. And we need to analyze the effect of the temperature on its output and resonance frequency.