Ampeg B-12N / B-15N Portaflex (1961) - Channel 1 preset

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

The March 1961 Ampeg B-12-N and B-15-N are two-channel Portaflex flip-top bass combos, differing mainly in speaker size. Channel one has two inputs and channel two one; each runs a 6SL7 gain stage, its own Bass and Treble network, a second 6SL7 stage and its own Volume. A 6SL7GT gain stage and paraphase inverter drive a cathode-biased pair of 6L6GTs with feedback from the 16-ohm tap, rectified by a 5U4GB, with a standby switch.

• Made in: USA
• Wattage: 25W
• Channels: 2
• Preamp tubes: 2× 6SL7, 1× 6SL7GT
• Power tubes: 2× 6L6GT

Known for: James Jamerson.

Tags: american, vintage, bass, 6l6, 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.