Posted by Damir [ 213.202.110.103 ] on December 02, 2005 at 07:37:20:
It can`t be measured successfully by ordinary capacitance meter, we must find it indirectly, finding self-resonant frequency of the inductor (scope and sig. generator, see for example "Valve amplifiers 3"-page 234). I can`t find many manufacturers data, all I can find are:
1.) On the "roehrentechnik.de" web pages, there are data for their two anode chokes:
-70H/1300 Ohms/Ce~300pF
-200H/2800 Ohms/Ce~90 pF (2 Kammer Wicklung)
Both chokes are good for 35-40mA at least.
2.) Measurements of (quality) S&B grid choke by Thorsten, see the link. He found Ce~65pF.
Well, 65p-90pF is not too much, but 300pF in parallel with 80pF input capacitance of 300B is 380pF. And with high impedance driver (cascode, pentode, high rp tubes common cathode...), say Rout~15kOhms, we have f-3= 1/(2*3,141*15000*380*10^-12) = 27,9 kHz , limited frequency response of the driver.
Do anybody has some more informations/measurements about "typical" shunt capacitance of grid/anode chokes?
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