| alejo |
Looking for info about like calculates capacitor value to bypass cathode in bias automatico; I find that:
when I now the value of cathode Resistor in ohms. it formulates:
Reactance=(1/50).Ohms
....to the Low Frecuency operate the circuit (for example at 20Hz.)
now, as the reactance of a capacitor for a given frequency calculates? |
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| Steve Eddy |
| quote: | Originally posted by alejo
Looking for info about like calculates capacitor value to bypass cathode in bias automatico; I find that:
when I now the value of cathode Resistor in ohms. it formulates:
Reactance=(1/50).Ohms
....to the Low Frecuency operate the circuit (for example at 20Hz.)
now, as the reactance of a capacitor for a given frequency calculates? |
1/(2 x pi x f x C)
Where f is frequency in Hertz and C is capacitance in Farads.
se |
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| alejo |
Thanks steve.
I confused because:
In one PushPull EL84/6BQ5 use for comon cathode resistor arround 140 Ohms
I want Bypass this resistor, and calculate:
Reactance=(1/50)*140
Reactance=2.8
Now find capacitor for 2.8 Ohms reactance at 20Hz
1/(2*pi*f*c)=
1/(2*3.141516*20* "test value capacitor in farads")=
for 2800uf
1/(2*3.141516*20*0.0028)=
2.84 Ohms
Ok. now;.... for correct bypass cathode resistor 140 Ohms at 20hz need 2800uF capacitor ?????
Please help !!!!! |
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| fdegrove |
Hi,
Actually the formula you should use is:
f = 1/(2*PI*R*C)
or: C = 1/(2*PI*F*R)
f = -3dB point.
R= Rk'//Rk
Rk' = (Rp+ra)/(mu+1) (Common-cathode stage)
Rp = Plate resistance
ra = Ri or internal resistance of the tube.
Rk = cathode bias resistor.
Note that C should always be much larger than Rk but not much larger than necessary for the lowest -3dB point wanted: t = R*C
Cheers, ;) |
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