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

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(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 -3dB frequency, Hz

Cathode Bypass filter response

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