For the brand, see Dynatron Radio Ltd

Dynatron Radio Ltd

Dynatron Radio Ltd was the trade name used by H.Hacker & Sons for their wireless products. The firm started trading in 1927 and operated independently until being bought by Ekco in 1955...

The dedicated dynatron vacuum tube

Vacuum tube

In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...

 was invented by Albert Hull

Albert Hull

Albert W. Hull is most remembered for his early invention of the magnetron.-Education and early career:...

 in 1918http://ieee.cincinnati.fuse.net/newsletters/200401.pdf. It has three electrodes: a thermionic cathode

Cathode

A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...

, a perforated anode

Anode

An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....

, and a supplementary anode or plate, and its characteristic curves have a region exhibiting negative resistance

Negative resistance

Negative resistance is a property of some electric circuits where an increase in the current entering a port results in a decreased voltage across the same port. This is in contrast to a simple ohmic resistor, which exhibits an increase in voltage under the same conditions. Negative resistors are...

, which is the property desired.

Other early vacuum tubes with four or more electrode

Electrode

An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...

s not designed for the purpose had significant secondary emission

Secondary emission

Secondary emission in physics is a phenomenon where primary incident particles of sufficient energy, when hitting a surface or passing through some material, induce the emission of secondary particles. The primary particles are often charged particles like electrons or ions. If the secondary...

 from the anode

Anode

An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....

, and, when operated with the anode at a lower voltage than another electrode, exhibited negative resistance and could be used as oscillators or for other functions. Later tubes had anodes treated to reduce secondary emission, normally an unwanted phenomenon, and were not suitable as dynatron devices.

Operation

In dynatron operation the supplementary anode is maintained at a lower positive voltage than the perforated anode. The secondary emission of electrons from the supplementary anode makes the dynatron behave as a true negative resistance, allowing it to be used to generate oscillations over a wide range of frequencies or as an amplifier. When a control grid was added between the cathode and the perforated anode, the device was called a "pliodynatron", with similar properties to a tetrode

Tetrode

A tetrode is an electronic device having four active electrodes. The term most commonly applies to a two-grid vacuum tube. It has the three electrodes of a triode and an additional screen grid which significantly changes its behaviour.-Control grid:...

 or pentode tube with significant secondary emission operated in dynatron mode.

Operation with a tube not designed specifically as a dynatron is described in the article on the dynatron oscillator

Dynatron oscillator

A dynatron oscillator is an electronic circuit that uses negative resistance to keep an LC tank circuit oscillating.In theory, if an ideal capacitor is connected in parallel with an ideal inductor, they form a resonant circuit that, once it begins oscillating, will oscillate forever as the energy...

.