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Old 2nd November 2011, 11:18 AM   #3011
sampler is offline sampler  Lithuania
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Quote:
Originally Posted by RCruz View Post
Perfect

Why did you choose J310 ?

Can it be replaced by k170 ?
You need much higher Vgs(off) and Ids (good headroom for lower fet), and reasonably low noise part for cascoding k170, at least it is what walt young tells us. PN4391 should be fine in this position too.

Last edited by sampler; 2nd November 2011 at 11:25 AM.
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Old 2nd November 2011, 01:21 PM   #3012
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Yes sampler, thats right. The 2SK170 needs at least some voltage over it and the higher the Idss in the cascode Fet ( J310 ), the better the regulation. I will look up PN4391.
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Old 2nd November 2011, 01:24 PM   #3013
Salas is online now Salas  Greece
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See also about K246 if in stash, else BF245B plenty in Europe.
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Old 2nd November 2011, 01:24 PM   #3014
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Sampler, this PN4391 is a very good find. Maybe even better then the J310.
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Old 2nd November 2011, 01:27 PM   #3015
Salas is online now Salas  Greece
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Don't know about the noise consistency of those chopper JFETs in production though. Had some ''happy'' ones from the ''J'' series in the past.
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Old 2nd November 2011, 01:34 PM   #3016
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I had no noise problem with J310. So far my favourite. BF245C should work too and as long as the 12V over the cascode are not eaten up a variety of other high Idss, high Vgs J-Fets.
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Old 2nd November 2011, 01:37 PM   #3017
Salas is online now Salas  Greece
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Yep, with the C variant you can be sure that IDSS will be high enough straight out of the stash without even looking.
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Old 2nd November 2011, 01:40 PM   #3018
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I am working on a power supply for the Nobrainer. I will publish it on the Nobrainer thread
in some hours.
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Old 2nd November 2011, 01:43 PM   #3019
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BF245C is plenty, so when that works well its a good substitute. One tip from me when you buy J310 : I found them as expensive as several € and as affordable then 20 €cents depending on supplier.
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Old 2nd November 2011, 01:50 PM   #3020
RCruz is offline RCruz  Switzerland
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Cool....

Are these jfets available or must I be carefull with fakes ?

Still fighting with the Riaa calc... Will keep posting
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Last edited by RCruz; 2nd November 2011 at 01:55 PM.
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