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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old Today, 07:15 PM   #96301
john curl is offline john curl  United States
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Scott is right, (see how I can be professional regarding you Scott?) the 2SK103 is usually much better than what you measured, perhaps 10dB better. The Y select (1.2-3ma) is the first clue. Try at least a GR or even a V in the same series and you will get better performance.
A good practical estimate of the jfet noise is to invert the working Gm of the part, in this case, 1/1000umho = 1000ohms = 4nV/rt Hz. Significantly more than that, you have a bad batch with very high 1/f noise. You have significantly more noise, so you have a batch or measurement problem.
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Old Today, 07:21 PM   #96302
EUVL is offline EUVL  Europe
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The test circuit (of Scott's design) includes an autobiasing mechanism so that ALL DUTs are tested with the same bias, around 1.2mA, irrespective of Idss.
We know it is working because it produces the expected noise level of a range of other JFETs, including 2SJ74, 2SK170, 2SK369, 2SK372, BF862, 2SK117 ......, etc.


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Old Today, 07:32 PM   #96303
john curl is offline john curl  United States
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Then, EUVL, you have a bad batch. This happens, even with Toshiba. Without a noise spec, they can get away with it in this case.
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