Kay K503A preset

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

The Kay K503A is a tiny practice amp built on radio-set lines, with series-wired heaters. Three inputs feed a 12AU6 pentode preamp, then a volume and a tone control (with the power switch on its pot) ahead of a single-ended, cathode-biased 50L6 beam tube driving the speaker through a small output transformer. A 35Z5 rectifier runs from an isolation transformer. Cheap and simple, it breaks up almost immediately, prized for lo-fi recording.

• Made in: USA
• Channels: 1
• Preamp tubes: 1× 12AU6
• Power tubes: 1× 50L6

Tags: american, vintage, low-wattage, practice.

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.