bypass cathode with cap and resistor..why?

[giordydiver]

hi guys looking afd100 schematic i have seen that the valve of afd mode has a bypass cathode formed by a cap in series with a resistor.. why use? ho cut off hight frequences?

[Haze13]

For AC the cap is a short circuit, so AC load line formed by a resistance of the 2 values in parallel... Of course very low frequencies are being filtered out.

[giordydiver]

if i understand in this way i have more gain but a fat and bass tone

[Haze13]

1/(2*Pi*r*C) = -3dB cut off frequency. r is a cathode resistor in parallel with a output cathode resistance (rk) of a tube.
rk= (RL (plate resistor) + ra (anode resistance of a tube )/(Mu + 1)

[giordydiver]

ok but which frequencies? hight or low?

[Haze13]

Put the values in the formula and calculate:) I don't know what cap and resistance are being used there...Most likely that a very low frequencies will be filtered out.

[giordydiver]

Ok, with 100n and 10k in series cutt off is at 83hz, but are cutted off frequencies over these or undere these? Sorry but i dont known a lot of theory

[Haze13]

Lower = Under