Harmony H-303A preset

verified · 92/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The Harmony H-303A is a tiny practice amp built on radio-style series-heater lines: a 12AU6 pentode preamp feeds a single-ended 50C5 output pentode, with a 35W4 rectifier fed from a small transformer. Three inputs share one volume control (with the power switch on the pot) and there is no tone control; it drives a 6-inch speaker at about 3 watts. It breaks up early and sounds small and midrangey, ideal for lo-fi recording.

Tags: american, vintage, practice, low-wattage, breakup.

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.