National-Dobro Concert 400 - Instrument preset

Verified · 84/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

The National-Dobro Concert Amplifier No. 400 (also sold as the Model 500) has separate instrument and microphone channels. Two 6J7 pentodes and two 6SC7 dual triodes drive a push-pull pair of 6V6s, with a 5U4 rectifier and a Jensen field-coil speaker, for about 15 watts.

• Made in: USA
• Wattage: 15W
• Channels: 2
• Preamp tubes: 2× 6J7, 2× 6SC7
• Power tubes: 2× 6V6

Tags: american, vintage, 6v6, 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.