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Replacement For Toshiba 2SK170/2SJ74
Replacement For Toshiba 2SK170/2SJ74
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Old 18th September 2019, 11:27 PM   #411
ticknpop is offline ticknpop  Canada
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Join Date: May 2005
Location: toronto
Replacement For Toshiba 2SK170/2SJ74
A reasonable idss match is better than 10%, some like 5 % , or even tigher, but it changes with temperature, even holding them in your fingers changes the idss,
. You need to let them stabilize in your idss test for a couple of minutes, with no breeze, and donít touch them , even changes in house temperature causes some drift, so measure them at the same time of day

The idss value you need depends on the circuit design.
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Old 21st September 2019, 06:49 AM   #412
astromo is offline astromo  Australia
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Join Date: Nov 2017
Location: BFN
Quote:
Originally Posted by Leicaphile27 View Post
I'd like to thank everyone for their helpful replies. Especially on how to measure IDSS. The Jfets I purchased from Spencer in Singapore haven't arrived yet. Measuring them should be straightforward. My question, however, is more along the lines of how much variance between the N and P channel is okay? Also, spec variance for BL grade range from 6-12...what it optimal and what happens the further you from optimal. Does it increase noise? Does sound quality deteriorate?
Refer here for the store's advice on JFET matching and the relevance of tolerance:

JFET matching information – diyAudio Store
Quote:
The JFET matching tolerance required for any of Nelson's projects is 1mA
You can fact check that detail through the various threads here and over at First Watt / PassDIY.

EDIT:
Fun fact / side-note - JFET guru, Erno Borbely, sold JFETs matched to 0.5 mA Idss according to the archived price list that I found:
https://web.archive.org/web/20100215.../Compprice.pdf

So, the noted comment from the store would not appear to be unreasonable.

Last edited by astromo; 21st September 2019 at 07:10 AM.
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