Clean Headroom / Max Output Wattage Estimator

Bench tool · draft

Clean Headroom / Max Output Estimator

Estimate clean and maximum clipping power from B+, load impedance, and tube type.

Estimate

Estimate only This is a simplified load-line approximation, not a lab measurement. Real output depends on transformer quality, bias point, rectifier sag, and how hard the driver stage can swing the grids. Use it to sanity-check a design or a datasheet spec — not as a substitute for measuring actual output on a dummy load with a scope. Ohm’s Law / Power Calculator Output Transformer Impedance Calculator Tube Bias Calculator Pro

Output tube Output stage topology B+ (plate supply voltage)

VDC

Plate-to-plate load impedance

Known amp reference (optional, auto-fills below) Global NFB resistor value (optional)

NFB tail / shunt resistor (optional, enables a real dB-based estimate)

What the NFB value can (and can't) tell this calculator With only the main NFB resistor entered, this nudges the clean/max ratio within a coarse, labeled range (65–82%) based on resistor value alone. With both the NFB resistor and its tail/shunt partner entered, the calculator instead estimates actual feedback dB from that divider ratio, assuming a typical open-loop gain (~8x) calibrated from published figures for one well-documented Fender circuit — a genuine estimate, not a measured value for your specific amp, since real open-loop gain varies by design. Leave both blank to use the flat 70% default.

— Approx. clean output (before audible compression)

— Estimated max output (into clipping)

— Clean output (dBW)

— Headroom, clean to clip (dB)

Po ≈ (B+ − V_knee)² / (2 × Z_pp) — clean estimate taken as ~70% of the clipping figure, a common rule-of-thumb margin before audible compression sets in.