Ampeg B-18N Portaflex - Channel 2 preset

Verified · 88/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The 1967 Ampeg B-18-N is the Portaflex bass combo built for an 18-inch speaker. Each of its two channels has a 6SL7 gain stage, its own Volume, a second stage and its own Bass and Treble network. They mix into a 7199 pentode gain stage and triode cathodyne inverter, driving a fixed-bias pair of 7027As with feedback from the 16-ohm tap. The rectifier is a 5AR4 valve, with a diode bias supply, standby, ground switch and an external-amp jack.

Known for: Jerry Jemmott.

Tags: american, vintage, bass, two-channel, mid-wattage.

Schematic-derived preset files for the Neural DSP Quad Cortex and 16 Fractal and Line 6 modelers: Axe-Fx II/XL/XL+, Axe-Fx III, FM3, FM9, and the full Helix family (Floor, LT, Rack, HX Stomp, HX Stomp XL, Native).

Gridleak extracts amp parameters from original circuit schematics using AI vision — component values, gain staging, tone stack topology, tube types — then generates native preset files for every supported modeler. Every extraction is scored 0–100 and the score is published.