Supro Thunderbolt S6420 - Normal preset

Verified · 82/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The Supro Thunderbolt S6420 is among the most powerful and recognizable Valco designs, originally marketed as a bass amplifier but widely adopted by guitarists for its raw, aggressive American character. Its bold attack, natural compression, and prominent upper midrange made it a distinctive tool for pushing guitar tones into natural overdrive. The Thunderbolt name became synonymous with American vintage amp tone at its most elemental.

• Years produced: 1962–1968
• Made in: USA
• Wattage: 35W
• Channels: 2
• Preamp tubes: 2× 12AX7
• Power tubes: 2× 6L6

Known for: Jimmy Page.

Heard on: Communication Breakdown — Led Zeppelin (1969).

Tags: american, vintage, crunch.

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.