Another high-perveance diode, the diode section of a 33GY7, shows similar perveance to a 6AL5, but handles 15 times greater current, at almost 13 times maximum peak inverse voltage.
2.
That is why it is used to form emitter-coupled amplifiers ( avoiding Miller effect ), phase splitter circuits ( obtaining two inverse voltages ), ECL gates and switches ( avoiding transistor saturation ), etc.
3.
Their low efficiency required a much higher forward voltage to be applied ( typically 1.4 to 1.7 V per " cell ", with multiple cells stacked so as to increase the peak inverse voltage rating for application in high voltage rectifiers ), and required a large heat sink ( often an extension of the diode's metal substrate ), much larger than the later silicon diode of the same current ratings would require.