Ampeg B-15S Portaflex - Channel 1 preset

Verified · 86/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The Ampeg B-15S is the higher-powered Portaflex bass combo, drawn in 1971. Each of its two channels has Bright and Normal inputs, a 12AX7 and its own Volume, Bass and Treble; channel one adds a three-position Bass/Flat/Guitar voicing switch. A 12DW7 mixes the channels and feeds an external-amp jack, then a 12AU7 long-tail phase inverter drives a fixed-bias pair of 7027As off a silicon bridge rectifier, with a switchable 2/4/8-ohm output.

• Made in: USA
• Wattage: 50W
• Channels: 2
• Preamp tubes: 2× 12AX7, 1× 12DW7, 1× 12AU7
• Power tubes: 2× 7027A

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

Schematic-derived preset files for 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.