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Old 28th January 2009, 09:51 AM   #2521
AndrewT is offline AndrewT  Scotland
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Hi,
clip the Gate lead on the Mosfet short, 2mm from the thick part.
Clip the gate resistor lead short, about 3mm, and solder this short end around the 2mm stub on the FET.
Attach the flex wire from resistor to PCB
Add your insulation sleeve over the gate stub/resistor/soldered flex lead end.

This very short connection from gate resistor to gate, reduces lead inductance. It's lead inductance between the gate and gate resistor that causes the oscillation.
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Old 28th January 2009, 10:54 AM   #2522
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OK,

thanks AndrewT and others.


Question: If I do change from resistor on PCB to resistor at mosfet, I just put in a link on the PCB where the resistor was?

And would 50R be ok instead of 47R (no more of them left and I have a good number of 100R dales I can parallel)


Gate would be pin 1 on both, right?


Fran
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Old 28th January 2009, 11:06 AM   #2523
AndrewT is offline AndrewT  Scotland
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or use 51r or 56r or 63r.
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Old 28th January 2009, 02:05 PM   #2524
labjr is offline labjr  United States
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Quote:
Originally posted by Peter Daniel


Both in F3 and now in F5 I'm using IXYS. Bought them years ago through the forum, but I guess Percy carries them too.

I intend to also try discrete diodes.
I take it you've compared the sound with these bridges in the power supply to regular ones?
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Old 28th January 2009, 02:55 PM   #2525
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Not really, I've heard they sound good, but never had a chance to compare them. Working with class A amps is different than with chip amps; parts swapping becomes much more complicated
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Old 28th January 2009, 07:39 PM   #2526
ichiban is offline ichiban  United States
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Quote:
Originally posted by jackinnj

TNX,
I have had to raise some prices -- I am out of my OLD stock on the IRF/Vishay HEXFET's -- and since Vishay took over IRF's discrete products the prices have really shot up. (Pretty unbelievable if you look at the bomb Intel laid on the market, but discretes is discretes.)

I think 1 shipment may have gone astray over Christmas -- have been away for 2 wks.
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I see matched pairs of 2SK170 and of 2SJ74 for sale under
"Small Signal Transistors and JFETs" but no matched 2SK170 to 2SJ74
pairs for sale? Would it be possible to order matched Ps to Ns? and at what cost?
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Old 28th January 2009, 08:20 PM   #2527
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Question Where do yo get your fets?

Where are you guys buying your 2sj108's and or 2sj74 from?
I'm not seeing them at Mouser or Digikey. Couldn't find much on the Net.
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Old 28th January 2009, 08:26 PM   #2528
tms0425 is offline tms0425  United States
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Mouser or Digikey don't carry them anymore. You might try Jackinnj these days. He provided nice full transistor kits for F4's and was great to deal with. I also got some j74 and k170BL's from www.ampslab.com last year.
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Old 28th January 2009, 08:36 PM   #2529
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I found 2sk170s at futurelec.com. They ship from Asia.
Used them in my B1 and tested fine. However, they mixed BL and GRs together. They don't have the 2sj108s.

I'll try others.
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Old 28th January 2009, 09:08 PM   #2530
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Quote:
Originally posted by ichiban

__________________________________________________ ___

I see matched pairs of 2SK170 and of 2SJ74 for sale under
"Small Signal Transistors and JFETs" but no matched 2SK170 to 2SJ74
pairs for sale? Would it be possible to order matched Ps to Ns? and at what cost?
I'm trying to peddle as fast as I can.

NP said that it is probably NOT a necessity to match the N and P channel JFET's for Idss or gm -- I don't want to second guess "the great one" but I need to demonstrate it for myself.

This is a remarkably simple and high quality DIY amp to get going -- and I have 4 of them in operation.
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