Secondary emission Dynatron oscillator

plate current ip , screen grid current ig2 vs plate voltage vp curves of rca s uy224 tetrode came out in 1929, showing negative resistance region (grey).

 screen grid potential vg2 = 75 v

 control grid potential vg2 = −1.5 v

in tube, secondary emission sufficiently strong not caused negative resistance (a declining slope) reversed plate current; more electrons left plate arrived @ it.

in electron tube, when electrons emitted cathode strike plate, can knock other electrons out of surface of metal, effect called secondary emission. in normal tetrode amplifier unwanted effect, , screen grid next plate biased @ lower potential plate, these secondary electrons repelled , return plate due positive charge.

however, if screen grid operated @ higher potential plate, secondary electrons attracted it, , return ground through screen grid supply. represents current of electrons ig2 away plate, reduces net plate current ip below cathode current ic

i

p


=

i

c


−

i

g
2





{\displaystyle i_{p}=i_{c}-i_{g2}\,}

higher plate voltage causes primary electrons hit plate more energy, releasing more secondary electrons. therefore, starting @ voltage @ primary electrons have enough energy cause secondary emission, around vp = 10v, there operating region (grey) in increase in plate voltage causes more electrons leave plate additional electrons arriving @ plate, , therefore net reduction in plate current.