Gibson GA-20 (6SJ7) - Instrument preset

Verified · 87/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

This version of the GA-20 is an early octal-valve Gibson combo with two channels, each with its own inputs, 6SJ7 pentode preamp stage and volume control. The channels mix into a tone control and a 6SL7 paraphase inverter, which drives a push-pull pair of 6V6GTs on a 5Y3GT rectifier, giving a warm, mid-forward tone that breaks up when pushed.

Tags: american, vintage, clean, crunch, 6v6.

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.