Univox U-255R preset

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

The U-255R is a Japanese-built Univox valve combo of the late 1960s. Mic, Guitar and Accordion inputs mix into one 12AX7 triode with a volume and tone control. Half a 12AT7 drives a spring reverb and the other half recovers it, with a level control and footswitch. A 12AX7 gain stage and phase inverter drive two 6973 power pentodes with negative feedback, and a 12AX7 tremolo with speed, depth and footswitch modulates their bias.

• Channels: 1
• Preamp tubes: 2× 12AX7, 1× 12AT7
• Power tubes: 2× 6973

Tags: 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.