Harmony H-420 preset

verified · 91/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The Harmony H-420 is a Valco-built bass and guitar combo, close kin to the Supro Thunderbolt but with a solid-state bridge rectifier, separate treble and bass controls and top-mounted controls. An accordion/mic input and two bass/guitar inputs mix into one 12AX7 triode and a volume control; a second 12AX7 amplifies and splits the phase for two cathode-biased 6L6GCs. Clean and full, with plenty of low end.

• Made in: USA
• Channels: 1
• Preamp tubes: 2× 12AX7
• Power tubes: 2× 6L6GC

Tags: american, vintage.

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.