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Sony Vfet Illustrated build guide
Sony Vfet Illustrated build guide
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Old 20th March 2018, 07:32 PM   #501
soundslave is offline soundslave  United States
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And...
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Old 20th March 2018, 07:39 PM   #502
soundslave is offline soundslave  United States
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I'm having as much success with the photos as I'm having with the amp
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Old 20th March 2018, 10:07 PM   #503
Dennis Hui is offline Dennis Hui  Canada
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Sony Vfet Illustrated build guide
Are P3 and P4 at minimium and are you getting around 4.3V between T7-T10 and T12-T9?
If so, what happens when you slightly start adjusting P3/ P4? (Actually start with P3) Can you
get The T18-G voltage to drop closer to 0?
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Old 20th March 2018, 10:47 PM   #504
soundslave is offline soundslave  United States
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Yes p3 and p4 are counterclockwise and I get 4.78v at both T7-T10 andT9-T12. I can adjust p3 to get less than 1v
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Old 20th March 2018, 10:55 PM   #505
Dennis Hui is offline Dennis Hui  Canada
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Sony Vfet Illustrated build guide
OK. That sounds good. I would now try the bias procedure.
Start at page 8 (Adjust P1 for T16....):

http://www.firstwatt.com/pdf/art_diy_sony_vfet.pdf
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Old 2nd April 2018, 07:41 PM   #506
jaab6 is offline jaab6  Canada
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After I changed the FQP3n0 and FQP3P30 from the BOM by matched 2SJ313 an 2SK2013
my problems are gone!
The voltage test point are fine. my problem right now is the vgs wrote
on one of the Sony vfet pair. One pair are readable 9.9 but the second pair I can just identify the 9, the second digit can be 1 4 7 or 9 .
I don't know whom to ask !
P1170003.jpg

P1170007.jpg

P1170008.jpg
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Old 2nd April 2018, 09:28 PM   #507
Dennis Hui is offline Dennis Hui  Canada
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Sony Vfet Illustrated build guide
You can be conservative and pretend it's 10V so set initial bias voltage at 11V.
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Old 3rd April 2018, 12:50 AM   #508
jaab6 is offline jaab6  Canada
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Doesn't matter if it's 9.1 and I set to 10?
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Old 3rd April 2018, 07:59 AM   #509
Dennis Hui is offline Dennis Hui  Canada
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Sony Vfet Illustrated build guide
Quote:
Originally Posted by jaab6 View Post
Doesn't matter if it's 9.1 and I set to 10?
If it's actually 9.1 and you pretend it's 10 and set the initial bias voltage
at 11, all that should happen is you will have to turn the bias pots more
to get current to flow during your installing vfet and adjustment procedure.

Since the vfet conducts more current as you decrease the bias voltage,
the idea of setting the initial bias voltage based the measured value of
the vfet is to make sure the current is low. If you know your parts are
9.X then setting the voltage at 11 is safe.
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Old 4th April 2018, 07:12 PM   #510
jaab6 is offline jaab6  Canada
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I took to much time writing my post and all have been lost!
we have similar values in g-t6 g-t8 and I changed r15 r16 to 46.4k but it's perhaps not necessary!
I would check again the resistors perhaps a 47.5k 47.5 has been inverted if not check the values of the trimers two are 500 ohms and two are 5k ohms. check if they are fully turned
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