Marshall JMP Bass 50 1986 - High Treble preset

Verified · 90/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The 1986 is the 50-watt bass head of the plexi-era range, the bass counterpart of the 1987 Lead. Two input channels feed two ECC83 stages and an ECC83 phase inverter driving two EL34s (6550s on the MkII), and guitarists often use it for its extra headroom.

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

Tags: british, vintage, bass, plexi, el34, mid-wattage, two-channel.

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.