Harmony H-303B preset

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

The H-303B is Harmony's revision of its smallest practice amp, again using the transformerless All-American-Five layout: 12AU6 pentode preamp, single-ended 50C5 output and 35W4 rectifier. Controls are a single volume (with the power switch on the pot) and it drives a 6-inch Jensen at about 3 watts. Expect early, fuzzy breakup and a narrow, boxy voice.

• Made in: USA
• Wattage: 3W
• Channels: 1
• Preamp tubes: 1× 12AU6
• Power tubes: 1× 50C5

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.