Gibson BR-4 - Microphone preset

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

The BR-4 is an early post-war Gibson amplifier with a microphone input on a 6SJ7 pentode stage with its own volume, and two instrument inputs sharing a second volume. Both feed a 6SL7 twin triode, followed by a tone control and a 6SN7 paraphase inverter driving a cathode-biased push-pull pair of 6V6s with feedback, on a 5Y3 rectifier with the speaker field coil as filter choke.

• Made in: USA
• Channels: 2
• Preamp tubes: 1× 6SJ7, 1× 6SL7, 1× 6SN7
• Power tubes: 2× 6V6

Tags: american, vintage, clean, 6v6.

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.