F5 power amplifier

Twitchie, I just noticed the drawing of 2sk370 is backwards, drain should go towards the + rail and source to ground. No big deal, the traces look fine.
If you make more boards you could also run the 240 source trace down the edge of the board and over to the .47 res. Then you could eliminate the drain jumper too, and just place the gate res across it.

Bill
 
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Thanks for all the kind words and words of encouragement. I just started a new job this week, so finding time to get back to this has been difficult.

about the drilling - I must be getting the cheap drill bits around here, or I must be overly aggressive in drilling because I always manage to snap my last one (doesn't matter how many backups I buy) before I finish all the holes :xeye:

Murphy's law rules around here with an iron fist (fist reference was not intentional). Another case in point - I pull my Proac clones apart to finally veneer them after running them 'au naturel' for years, and end up getting delayed by having my hex-head wood screw order lost by Canada Post ...

An externally hosted image should be here but it was not working when we last tested it.
 
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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Re: GR, BL, V?

panos29 said:
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.
 
consider paralleling GR JFETs

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

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

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Re: GR, BL, V?

Nelson Pass said:


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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Re: Re: GR, BL, V?

plep said:
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.