Metasonix – R-53 Vacuum-Tube Waveshaper / Ringmod module
“… uses a 12AF6/BD6 remote-cutoff pentode and a 12AV7 dual triode.
Waveshaping is provided by a vacuum-tube “pulser” circuit that spits
irregular pulses onto the input waveform. They synchronize erratically
with the input pitch (if a waveform with sharp transitions is used).
Combined with true vacuum-tube circuit distortion, this can provide a
vast range of complex, aggressive distortion effects, utterly unique in
the world. A basic ring-modulation function is also available in the
unit–applying a carrier pitch from an external oscillator to the screen
grid of the pentode, this allows making inharmonic sum-and-difference
pitch sound effects, with a unique vacuum tube pentode sound. “