Positive Slew Generator

The ES09 can be used as both a rising slew rate controller, or a upwards sloping ramp LFO by hooking the lower pulse out into the Start input. In this configuration it also operates as a utility oscillator, suitable for fixed key sequencing and general sound effects and noise making. It is not suitable for tracking a keyboard.

The slew rate is adjustable from ~500uS to ~17 seconds.

https://www.elby-designs.com/webtek/euro-serge/es09-positive-slew/es09.htm