Cathode Bypass Capacitor Calulator
Cathode bypass capacitor calculator

The cathode bypass capacitor in tube amp forms a filter that reduces the low frequency gain of the a common cathode amplifier. This calculation is based on Langford Smith's formula from Radiatron Designers Handbook 4. You will need to look up the data for the particular tube your are using. The defaults are typical for a 12AX7

You can type in the boxes or drag the sliders




(1) mu, from datasheet
(2) Total effective plate load resistance, k ohms
(3) Plate resistance, k ohms from datasheet
(4) Cathode resistor Rk, k ohms
(5) Desired half boost frequency, Hz

Cathode Bypass filter response


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