| Re: Choke capazitance, round 2 [message #31855 is a reply to message #31852] |
Wed, 29 March 2006 05:01   |
Damir
Messages: 1005
Registered: May 2009
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Illuminati (2nd Degree) |
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I posted about it in the "Tubes" section some time ago. If we have pentode or cascode stage with, say 15k load and internal resistance of 100k, then "effective" load is 15k//100k = 13k.
If our driver has, say S=4mA/V and grid choke as a load, then amplification on some higher frequencies, say 1kHz is A= S*Ra = 13*4 = 52 times. Choke impedance on 1kHz is theoretically Z = 2Pi*f*L = 2Pi*1000*650 = 4Meg >> 13kOhms.
But, on low frequencies, say 40Hz, our choke impedance is only 163,3k and our amplification is now: A = S * (13//163,3) = 4*12 = 48 times.
Although it is only 0,7dB of difference, I`m pretty sure that it is audible. Plus falling of highest frequencies `cos of low pass filter formed with Rout of the driver and Cw.
What you think about actual measurements of frequency response in real amp with real components (grid chokes) ? 
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