Free workshop tool
Plate Dissipation Calculator
Convert measured plate voltage and plate current into watts and percentage of a valve’s maximum rated plate dissipation.
Measurement note Use plate-to-cathode voltage where possible. If your probe measures cathode current, remember that cathode current can include screen-grid current, so it may read slightly higher than true plate current.
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View Valve Bias Pro →Formula
How it is calculated
Plate dissipation in watts
Plate dissipation = plate-to-cathode voltage × plate current in amps. Example: 450 V × 0.035 A = 15.75 W.
Percentage of maximum rating
Dissipation percentage = calculated plate watts ÷ the valve’s maximum plate dissipation × 100.
Is 70% always the correct target?
No. 70% is commonly used as an upper reference for many class-AB fixed-bias guitar amplifiers, not a universal setting. The amplifier design and valve datasheet remain the authority.