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Old 30th November 2010, 11:02 PM   #31
chip_mk is offline chip_mk  Macedonia
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Well, then what do you think, what could be that bl**dy thing in the corner?

- It looks like 2-3mA @1.5V Vgs
- It rises at lower Vgs
- It isnt dotted line meaning its measured at 25C

As temperature rises the curve moves to the left and Ig becomes immeasurable, in most cases. Spavleski has apparently OK device but it shows some measurable Ig that disappears after warm up. Could it be an expected behavior with variations from device to device? Or simply the chart is misprinted?
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Old 30th November 2010, 11:15 PM   #32
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by spavleski View Post
At the moment Bias is set to Id = 1,85A and Vds = 20V with inputs grounded. Sound is
sound - with inputs grounded ?

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Old 30th November 2010, 11:16 PM   #33
chip_mk is offline chip_mk  Macedonia
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Quote:
Originally Posted by spavleski View Post
Seriously speaking , most probably it is about bad contact connection during measurements. Soon I will replace 3W resistors with a MOX type, and will take out the boards and will re-check one more time.
Sorry to bother, would you care (for the sake of science) to measure Vgs along with Igs next time? It seems Ig becomes measurable at cold start and with lower Vgs (is it too complicated to try it with lower bias current?).

Last edited by chip_mk; 30th November 2010 at 11:17 PM. Reason: Correction
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Old 30th November 2010, 11:20 PM   #34
Zen Mod is offline Zen Mod  Serbia
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I have impression that Papa already said his results ........ and he certainly have more specimens to play with

I know for 12 pcs of SSouths in entire Serbia

even if you triple that .... it's funny
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Old 30th November 2010, 11:58 PM   #35
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Quote:
Originally Posted by chip_mk View Post
Sorry to bother, would you care (for the sake of science) to measure Vgs along with Igs next time? It seems Ig becomes measurable at cold start and with lower Vgs (is it too complicated to try it with lower bias current?).
I'll play a bit soon (in a week or two), during MOX replacement. Will post findings here.
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Old 1st December 2010, 12:00 AM   #36
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Quote:
Originally Posted by Zen Mod View Post
sound - with inputs grounded ?



After Bias setting and connecting some music
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Old 27th November 2011, 11:29 AM   #37
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Exclamation Any news ?

Yesterday I found the same problem in my new tube / Jfet project. Using a pair of the SJEP120R100A having highly different gate input currents :-( The driver is a 6SN7 @ 8 mA cathode follower. It seems to work after 30 minutes screwing at the pots and increased heatsink temperature....
Looks like this strong variation in the Jfets will needs extra attention...

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Old 2nd March 2013, 12:46 PM   #38
EUVL is offline EUVL  Europe
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We were very lucky to be able to get hold of a sizable batch of SJEP120R100s.
Today we took 9 of them out at random, and curve traced them.
Vds was 25V, and case held at 25C by a huge block of aluminium.
No time to heat up to 60C today.

You can judge for yourself the chances of getting good match sets with a small matching pool.
At current asking prices, rejects will be horrendously expensive.


Patrick
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Old 2nd March 2013, 12:57 PM   #39
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EUVL,
While Vgs defintely appears to be all over the place, have you had a chnce to check for consistency of Yfs? I have 8 that are pretty well matched, just have to check their yfs. Also, will you be checking for leakage?
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Old 2nd March 2013, 01:57 PM   #40
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If you cannot find proper Vgs pairs, why would you bother with the other two parameters ?


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