National-Dobro Model 21 / Model 31 preset

Verified · 86/100 confidence. Complete schematic. All component values readable. Parameters derived directly from the circuit.

This page covers two National-Dobro amps from the same service-manual sheet. The Model 21 (1939) is a small AC amp with a 6J7 pentode and 6F5 triode preamp driving a single-ended 6V6, with a type 80 rectifier, a field-coil speaker and a volume control only. The Model 31 is a low-voltage version built around battery-type tubes (1G6G, 1C5G) with a permanent-magnet speaker.

• Made in: USA
• Channels: 1
• Preamp tubes: 1× 6J7, 1× 6F5
• Power tubes: 1× 6V6

Tags: american, vintage, class-a, low-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.