THD Flexi-50 preset

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

The THD Flexi-50 is a 50-watt single-channel head that runs 6L6, EL34 or 6550 output valves, with an individual bias pot for each and a Hi/Lo voltage switch. Two 12AX7 stages with bright and sensitivity switches feed a treble/middle/bass stack and an effects loop, then a relay-switched boost with its own level and tone. A 12AX7 long-tail inverter with two footswitchable master volumes drives the pair, with an impedance switch and a transformer-isolated line out.

• Made in: USA
• Wattage: 50W
• Channels: 1
• Preamp tubes: 3× 12AX7
• Power tubes: 2× 6L6/EL34/6550

Tags: american, boutique, crunch, mid-wattage.

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.