Ampeg SVT (1972, 6550 Tube) - Channel 1 Bright preset

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

From 1972 onward, the Ampeg SVT transitioned from 6146B to 6550A output tubes, a change driven by parts availability and the superior power handling of the 6550 in push-pull bass amplifier circuits. The 6550-equipped SVT produced the same 300 watts as the original 6146B version but with a slightly different sonic character — often described as tighter and more harmonically complex in the midrange. This version became the most-produced and most recognizable SVT variant, setting the sonic template that all subsequent SVT designs would reference.

• Years produced: 1972–1980
• Made in: USA
• Wattage: 300W
• Channels: 2
• Preamp tubes: 6× 12AX7, 2× 12DW7
• Power tubes: 6× 6550A

Known for: John Entwistle, Geezer Butler, Lemmy Kilmister, Geddy Lee, Roger Waters.

Heard on: Physical Graffiti — Led Zeppelin (1975); 2112 — Rush (1976).

Tags: american.

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.