What tubes does the Supro Thunderbolt S6420 (Late 1966) use?

The Supro Thunderbolt S6420 (Late 1966) uses 2× 12AX7 preamp tubes and 2× 6L6GC power tubes.

When was the Supro Thunderbolt S6420 (Late 1966) produced?

The Supro Thunderbolt S6420 (Late 1966) was produced 1964–1967.

Supro Thunderbolt S6420 (Late 1966) preset

Verified · 93/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The Supro Thunderbolt S6420 is a late-1960s bass amp with a famously simple circuit. Two inputs feed one 12AX7 stage, then 500K volume and tone controls, a second 12AX7 gain stage, and the other half of that valve as a paraphase inverter. Two 6L6GCs share a 200-ohm cathode resistor (cathode bias, no negative feedback) on a four-diode 1N4007 bridge at about 390 V. Guitarists prize it for loud, raw, unforgiving breakup.

Years produced: 1964–1967
Made in: USA
Wattage: 35W
Channels: 1
Preamp tubes: 2× 12AX7
Power tubes: 2× 6L6GC

Tags: american, vintage, 6l6, bass, crunch.

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.