input resistor on the JE LAB 300B - Page 2 - diyAudio
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Old 21st December 2010, 04:38 PM   #11
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My 2 cents that you don't need an input cap.
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Old 21st December 2010, 04:38 PM   #12
cjkpkg is offline cjkpkg  United States
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Maybe I wasnt clear...below is the schematic I mostly used...very similar to the JEL300b...I also ADDED the 300 ohm grid stopper going from input or top of the 100k grid resistor to the grid of the 6sn7.
Click the image to open in full size.
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Old 21st December 2010, 04:49 PM   #13
ixe13 is offline ixe13  Canada
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Oh cool,

A picture...

I was looking of a way to draw what I thought I understood and show it to you guys.

I wasnt far.

A grid stopper? Is it gonna attenuate the input a bit?

Although 300 Ohms is not much and preventing oscillation is not a bad thing...
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Old 21st December 2010, 04:57 PM   #14
cjkpkg is offline cjkpkg  United States
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I have been researching this a little lately and from what I understand - however correctly - the grid resistor will have more or less of an attenuating effect at the cost of bandwidth versus the grid stopper. Increase value = increased attenuation & decreased bandwidth

Typical values for the grid stopper are from 200ohm - 1kohm...from what I have seen and has little to no effect on attenuation and are presumed optional.
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Old 21st December 2010, 05:06 PM   #15
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I would not be afraid of using no grid stopper at all here.
After all a 6SN7 is not a high transconductance tube.
Grid stoppers are really necessary with high transconductance tubes like 6922, 5842 and others.
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