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Old 7th May 2008, 10:41 AM   #631
panos29 is offline panos29  Greece
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Default GR, BL, V?

So, which of the 2SK170/2SJ24 versions is more suited to the F5 schematic as proposed, GR, BL or V? I know this is a silly question but to tell the truth, its the first time I am dealing with Jfets and I am getting a little confused here.
I am sure that Mr. Pass specified everything (as usual) in his article in AudioXpress, but in this part of the world the May issue is not yet available and I am already gathering parts...

Thanks
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Old 7th May 2008, 10:46 AM   #632
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No GR !
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Old 7th May 2008, 11:34 PM   #633
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I made a mistake which Ole pointed out, the schema is changed to reflect the correct S and D connections.

Here's a 3D hypothetical using some Caddock TO-220 feedback resistors which will attach to the heat sink:

Click the image to open in full size.
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Old 7th May 2008, 11:44 PM   #634
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Default Re: GR, BL, V?

Quote:
Originally posted by panos29
So, which of the 2SK170/2SJ24 versions is more suited to the F5 schematic as proposed, GR, BL or V? I know this is a silly question but to tell the truth, its the first time I am dealing with Jfets and I am getting a little confused here.
I am sure that Mr. Pass specified everything (as usual) in his article in AudioXpress, but in this part of the world the May issue is not yet available and I am already gathering parts...

Thanks
You want to test Idss for 8+ ma current with the Gate and Source
shorted and Vds at 10V.

BL is the preferred part, but you can use GR if you raise the
Drain resistance. Currently its a 5K pot, in parallel with a thermistor
plus 2.2K in parallel with a 2.2K. You can remove the 2.2K.

Alternatively you can consider paralleling JFETs to get the current up.
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Old 8th May 2008, 07:52 AM   #635
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Quote:
consider paralleling GR JFETs
There's a thought.
..........Naah.

(howcome, even in walnut veneer i see naked women?)
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File Type: jpg grrrr2.jpg (59.0 KB, 2606 views)
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Old 8th May 2008, 08:07 AM   #636
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by jacco vermeulen

.....

they are sad
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Old 8th May 2008, 01:34 PM   #637
DaveM is offline DaveM  United States
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(howcome, even in walnut veneer i see naked women?)
Because you are a man.
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Old 8th May 2008, 04:04 PM   #638
plep is offline plep  Belgium
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Default Re: GR, BL, V?

Quote:
Originally posted by Nelson Pass


You want to test Idss for 8+ ma current with the Gate and Source
shorted and Vds at 10V.

BL is the preferred part, but you can use GR if you raise the
Drain resistance. Currently its a 5K pot, in parallel with a thermistor
plus 2.2K in parallel with a 2.2K. You can remove the 2.2K.

Alternatively you can consider paralleling JFETs to get the current up.

Taking the risk to appear publicly too stupid…

Why V grade with a lower R wouldn’t work?
I'm afraid that it would reduce the open loop gain, but the same goes for GR the other way round (I mean increase the OLG with GR).
Best regards.
Philippe.
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Old 8th May 2008, 04:28 PM   #639
Magura is offline Magura  Denmark
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Quote:
Originally posted by jacco vermeulen


There's a thought.
..........Naah.

(howcome, even in walnut veneer i see naked women?)

So you're offering a group buy od 2sk147

The answer to your question may be due to Jaccolina or the lack of

Magura
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Old 8th May 2008, 04:30 PM   #640
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Default Re: Re: GR, BL, V?

Quote:
Originally posted by plep
Why V grade with a lower R wouldn’t work?
I'm afraid that it would reduce the open loop gain, but the same goes for GR the other way round (I mean increase the OLG with GR).
Best regards.
Good question. The amp will work fine with V. I neglect it for two
reasons.

1) try and find any, and if you do, save them for phono stages

2) I want to limit the current to about 8 ma through the circuit to
avoid too much dissipation in the JFET. Of course you can use a
greater value than the 10 ohm for the feedback, but you can
just as easily get by with a BL.
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