Folded Cascode Hijinks with PN4391 - Page 4

wrenchone · 26th December 2011, 11:28 PM

Here's a picture of the board in question in a clamp on the bench, getting ready for gain-phase measurements. Schematic will follow in a bit.

wrenchone · 26th December 2011, 11:33 PM

Here's the gain-phase plots. The 1kHz gain between the two channels is off by ~0.4 dB. I'll be trying to bring that closer by better matching between jfets and also for the current sources feeding them. Meanwhile, I want to throw the current revision preamp into my system to see if the extra care will be worthwhile.

wrenchone · 20th January 2012, 05:26 AM

I picked up 100X NSC 2n4391s from a Chinese E-pay seller - It'll be interesting to see how they test out. The NSC PN4391s I've tested have so far been on the "hot" side in terms of Vgs for a modest drain current.

wrenchone · 2nd February 2012, 11:09 PM

Hese's the 4391s I got from a HK E-pay seller. I wish I had bought more of them when they were as common as dirt ~20 years ago...

bcarso · 2nd February 2012, 11:38 PM

Apparently National Semi if they are genuine. Can you decode the date of manufacture?

wrenchone · 2nd February 2012, 11:52 PM

Date code may be 9411. I don't know when National unloaded their discrete lineup, but if this date is after that, then they would be fakes. I don't see why anyone would bother to put fake fets in gold-plated TO-18 packages, though, unless these parts are some other device that was scrubbed clean and re-marked. I plan to put a couple through my fet tester to see if they make noises like a typical 4391. This may not happen until I get back from a business trip to China. If they are legit, I have just the heat sink for them...

bcarso · 2nd February 2012, 11:58 PM

I suspect they are real.

wrenchone · 3rd February 2012, 12:11 AM

I did a little digging using Google, and it appears that National dumped their discrete lineup in 1996 when they spun off Fairchild as a separate entity.

bcarso · 4th February 2012, 09:41 PM

If those are still available I'd be interested in the contact. Also, if you find it convenient I'd like to know what their typical drain-source breakdown voltage is running (don't destroy one in the process, but say when does the drain-gate zener with a 10M resistor in series?).

Clearly, I don't have these in mind for a production run

Brad

wrenchone · 12th February 2012, 05:30 AM

Easy, just search for 2N4391 on E-pay. The source is the only one offering National 2N4391 in quantity. The price is merely obscenely extortionate as compared to hilariously extortionate. If these are real 4391s, they are rated for 40V, though no doubt some will break down at a higher voltage.

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20th January 2012, 05:26 AM	#33
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	I picked up 100X NSC 2n4391s from a Chinese E-pay seller - It'll be interesting to see how they test out. The NSC PN4391s I've tested have so far been on the "hot" side in terms of Vgs for a modest drain current.

2nd February 2012, 11:38 PM	#35
bcarso diyAudio Member Join Date: May 2005 Location: Canoga Park, California	Apparently National Semi if they are genuine. Can you decode the date of manufacture?

2nd February 2012, 11:52 PM	#36
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	Date code may be 9411. I don't know when National unloaded their discrete lineup, but if this date is after that, then they would be fakes. I don't see why anyone would bother to put fake fets in gold-plated TO-18 packages, though, unless these parts are some other device that was scrubbed clean and re-marked. I plan to put a couple through my fet tester to see if they make noises like a typical 4391. This may not happen until I get back from a business trip to China. If they are legit, I have just the heat sink for them...

2nd February 2012, 11:58 PM	#37
bcarso diyAudio Member Join Date: May 2005 Location: Canoga Park, California	I suspect they are real.

3rd February 2012, 12:11 AM	#38
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	I did a little digging using Google, and it appears that National dumped their discrete lineup in 1996 when they spun off Fairchild as a separate entity.

4th February 2012, 09:41 PM	#39
bcarso diyAudio Member Join Date: May 2005 Location: Canoga Park, California	If those are still available I'd be interested in the contact. Also, if you find it convenient I'd like to know what their typical drain-source breakdown voltage is running (don't destroy one in the process, but say when does the drain-gate zener with a 10M resistor in series?). Clearly, I don't have these in mind for a production run Brad

12th February 2012, 05:30 AM	#40
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	Easy, just search for 2N4391 on E-pay. The source is the only one offering National 2N4391 in quantity. The price is merely obscenely extortionate as compared to hilariously extortionate. If these are real 4391s, they are rated for 40V, though no doubt some will break down at a higher voltage.

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