Ampeg SB-12 Portaflex (7868 version) - Instrument preset

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

The SB-12 Portaflex with 7868 output tubes is an unusual variant of the flip-top series using the 7868 octal beam tetrode. The Instrument channel is voiced for bass guitar with a warm, full-range response. The 7868 tubes provide a similar power output to 6L6 but with slightly different harmonic characteristics.

• Years produced: 1964–1968
• Made in: USA
• Wattage: 30W
• Channels: 2
• Preamp tubes: 3× 12AX7
• Power tubes: 2× 7868

Tags: bass, american, vintage, low-wattage, clean.

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.