Marshall JCM800 Bass 50 1986 preset

Verified · 88/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The JCM800 Model 1986 is Marshall's 50-watt valve bass head of the early 1980s. High and low inputs feed an ECC83 with volume, middle and a mid sweep, then a cathode-follower bass and treble stack and a slope control. An ECC83 long-tail phase inverter drives two EL34s (6550s on US models), with a standby switch and 4, 8 and 16 ohm outputs.

• Made in: UK
• Wattage: 50W
• Channels: 1
• Preamp tubes: 3× ECC83
• Power tubes: 2× EL34

Tags: british, bass, el34, 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.