~ un bypassed Cathode Calculator ~

 This Calculator is to support my Amplifier–Buffer project and can be used to calculate the gain of a triode amplifier using a common cathode gain stage with a cathode follower output buffer so the overall gain is not significantly affected by the output load The results update as new input values are entered ~ Values for gm ra and µ should be taken from the valve characteristics or manufacturers data ~ The default values are for an ECC81 with V1 Ia ≈1mA and Cathode follower V2 Ia ≈2.3mA ~ ra1' and gm1' are for information only to indicate how Rk affects µ and gm I have also included an anode load for the cathode follower stage so the effect of such can be seen or the output ARL2 can be used to calculate the gain of a split load phase splitter when RL2 and RK2 are the same value so the outputs are the same level but in anti–phase ~ Click here for other calculators Variables for gain stage V1 Mutual conductance — gm1 mA/V  —  See notes below Internal anode resistance — ra1 kΩ Amplification factor — µ1 = gm1 x ra1 Anode load resistor — RL1 kΩ Cathode resistor — Rk1 kΩ Calculated results for V1 gain stage Rk modified ra1 — ra1' kΩ  =  ra1+ (µ+1) Rk1 Rk modified gm1 — gm1' mA/V  =  µ1 / ( ra1+ (µ1+1) Rk1) Unloaded voltage gain — AV1 =  µ RL1 / ( RL1+ ra1+ (µ1+1) Rk1) Unloaded voltage gain — AV1 dB  =  20log(Av1) Output resistance at V1 anode kΩ  =  ra1'||RL Variables for cathode follower V2 Mutual Conductance — gm2 mA/V  —  See notes below Internal Anode Resistance — ra2 kΩ Amplification Factor — µ2 = gm2 ra2 Anode Resistor — RL2 kΩ Cathode Resistor — Rk2 kΩ Calculated results for Cathode Follower V2 Gain at V2 anode — ARL2 =  µ2 RL2 / ( RL2 + ra2 + (µ2+1) Rk2) Gain at V2 cathode — ARk2 =  µ Rk2 / (RL2 + ra2 + (µ2+1) Rk2) Output resistance at V2 Cathode — Rout Ω  =  (ra2+RL2)  / (µ2+1)||Rk2 Overall voltage gain at V2 Cathode dB = 20log(Av1ARk2) The value entered for gm is not used to calculate results but is used to calculate the value µ = gm x ra which should be close to the entered value of µ for the results to be valid ~ As with most calculations with triodes gm and gm' could be used but ra' would also be needed ~ the factor (µ+1) helps simplify things ~ a little bitIt is assumed the bias is optimised for both the gain stage and follower and that separate values for gm ra and µ have been found and entered for both stages and that a sensible Ia and HT voltage have been chosen for the Va used ~ Click here for other calculators