Stromberg-Carlson AP-80 preset

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

The Stromberg-Carlson AP-80 is a valve PA power amplifier with no tone controls. A single input and Volume feed a 12AT7 with two gain stages and global negative feedback from the output transformer, then a 12AU7 phase inverter that drives four 6550 beam tetrodes push-pull in fixed bias with a Bias Adjust control. The high-voltage supply uses two 5R4GY rectifiers and a 5Y3GT, about 620 V on the plates, and the output transformer has 4-ohm, 25 V and 70 V line taps plus a relay connection.

• Made in: USA
• Wattage: 80W
• Channels: 1
• Preamp tubes: 1× 12AT7, 1× 12AU7
• Power tubes: 4× 6550

Tags: american, vintage, power-amp, 6550, high-wattage, clean.

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.