Available as an assembled Module and as a DIY project.
This Module is currently available.
VCF built on VLT5C Vactrols. A real old school analog VCF sound
An analog Voltage Controlled Filter with Band Pass, Low Pass and High Pass outputs and voltage controlled resonance.
The vactrols have a short 'memory' and the relationship between the Control Voltage and the output frequency is not perfectly linear, so this module can introduce interesting artefacts and textures into your sound. Additionally, the resonance is on steroids. You have full control all the way from none, tasteful, sine wave, up to a nasty clipped 'square wave' resonance.
https://www.tindie.com/products/nbirch/vactrol-vcf-for-eurorack-6hp/