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Old 11th October 2014, 05:40 AM   #1
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Default Calculating cathode follower using 12AU7 for 90V supply

Hi everyone,

Need help calculating resistors for cathode follower. Here is schematics:
Click the image to open in full size.

Power supply will be 90V.
My estimate values:
RL = 3 kOhm
RB = 200 Ohm
RG = 100 kOhm

Cin = 2uF
Cout = 2uF
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Old 11th October 2014, 06:24 AM   #2
JMFahey is offline JMFahey  Argentina
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For close to 45V on cathode, Rb=390r and Rl=18k

From:
Click the image to open in full size.

Ignore the red line, I just "borrowed" this graph from another page.
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Old 11th October 2014, 06:40 AM   #3
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Why 45V?
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Old 11th October 2014, 06:53 AM   #4
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Quote:
Originally Posted by gooduser View Post
Need help calculating resistors for cathode follower...
Essential design information missing. Maximum signal level and load impedance.
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Old 11th October 2014, 07:18 AM   #5
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45V is half of your 90V B+. Generally the best place to start. Blue line.
Attached Images
File Type: jpg 12AU7 plate curves.jpg (340.0 KB, 189 views)

Last edited by jerluwoo; 11th October 2014 at 07:28 AM.
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Old 11th October 2014, 07:21 AM   #6
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Load impedance 980 Ohm, max input level - CD or iPod
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Old 11th October 2014, 07:31 AM   #7
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Quote:
Originally Posted by gooduser View Post
Load impedance 980 Ohm, max input level - CD or iPod
Hope you like distortion.
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Old 11th October 2014, 07:35 AM   #8
freddi is offline freddi  United States
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ideally Rk like a plate load resistor, should equal 2Xrp at the operating point - that's an awfully low Z but not a lot of voltage to swing
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Old 11th October 2014, 08:02 AM   #9
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I'm assuming I should either increase voltage or load resistance? What would those be for operating without "distortion"? Thank you.
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Old 11th October 2014, 08:10 AM   #10
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Would increasing load resistance to 1.8k help?
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