VCA with a Russian mini-tube, featuring a feedback circuit and a bias voltage switch.
A VCA module using a Russian mini-tube, made by Klangbau Köln.
It features a gain knob and a three-way switch for the tube's bias voltage (to achieve a different saturation sound), a CV input, two audio inputs and an audio output - all with attenuators.
The second audio input is normalled to the first input, which lets you add feedback.
http://www.xn--klangbaukln-zfb.de/vca/
No info about availability.