Audio synthesis via vacuum tubes/Using sheet-beam tubes (view source)
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The sheet-beam tubes were modified pentodes. Between the suppressor grid and a pair of matching anodes, there were placed two beam-deflection plates. By putting a push-pull modulation AC signal across these two deflection plates, the electron beam could be "forced" to switch from one anode to the other; giving a very good ring modulator effect, with reasonable carrier suppression (provided the input and modulation signals were fairly high in peak voltage). So far, this sounds similar to the differential-amp balanced modulator seen in IC form.<ref name="usbdt"/>
However, the tube has something the IC doesn't.......... a screen grid. By varying the screen voltage between the plate supply voltage and the actual plate idle voltage, drift effects take over, and the peaks of the waveform start to fold over on themselves. Moreover, this folding is not sharp, as in the famed [[Ken Stone/1973 classic Serge/Serge tripple wave-shaper|Serge waveshaper]] circuit of the 1970s. It also happens on top of the modulation, causing some very strange and distinctive effects.<ref name="usbdt"/>
== Circuits ==
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