Ampeg SVT Power Amp (6146B) - Normal preset

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

The earliest SVT power amps used 6146B beam tetrode tubes rather than the later 6550A. This schematic documents that original output stage configuration. The 6146B version has a slightly harder, more aggressive character compared to the 6550A variant, and is prized by collectors as the most authentic early SVT tone.

• Years produced: 1969–1971
• Made in: USA
• Wattage: 300W
• Channels: 1
• Preamp tubes: 2× 12AU7
• Power tubes: 6× 6146B

Known for: Paul McCartney, Geddy Lee, John Entwistle, Lemmy Kilmister, Geezer Butler, Cliff Burton.

Heard on: Won't Get Fooled Again — The Who (1971).

Tags: bass, american, vintage, high-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.