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Sony Vfet Illustrated build guide
Sony Vfet Illustrated build guide
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Old 1st July 2020, 03:32 PM   #1091
Jim50hertz is offline Jim50hertz  United Kingdom
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Ok, so I was able to confirm orientation from datasheets, where I should have gone in the first place!

I've powered up both boards, and with 510r in r34/35 I get around 4.7v across both r34/35 on both boards.

How do I ascertain Jfet idss from this and adjust r34/35?

My voltages are way off from the initial voltages as noted by Nelson. I'm using the Fairchild JFets

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Old 1st July 2020, 03:43 PM   #1092
Dennis Hui is offline Dennis Hui  Canada
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Sony Vfet Illustrated build guide
There are no source resistors on the jfets so there are running at Idss.

So the voltage drop across R34/R35 is just the Idss times the resistance.
So the current is 4.7V/510 ohm ~ 9.2mA
A lot of numbers are different because with 510R for R35/R34 your mosfets are
now on. (See T6-T7 and T8-T9 voltages).

But things like G-T6 and G-T8 shouldn't change since those are just the rail voltages.
G-T4 and G-T2 also shouldn't change.

Please check these, as well as your raw DC rail voltages.
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Last edited by Dennis Hui; 1st July 2020 at 03:53 PM. Reason: More test points
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Old 1st July 2020, 04:10 PM   #1093
bajjisw is offline bajjisw  United States
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And please post a picture of your power supply, especially input and output connections.
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Old 1st July 2020, 04:15 PM   #1094
Rodeodave is offline Rodeodave  Austria
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Sony Vfet Illustrated build guide
Something's not right. G-T6 should be pretty much the full positive supply voltage of 28V.

We need to see pics of the PSU, including transformer wiring.
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Old 1st July 2020, 04:19 PM   #1095
Jim50hertz is offline Jim50hertz  United Kingdom
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I'm using a bench PSU. This one.

Is this not useable for the task?

Voltages are the same upon checking Dennis
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Old 1st July 2020, 04:24 PM   #1096
Ben Mah is offline Ben Mah  Canada
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Sony Vfet Illustrated build guide
That is a 0-30V or 15V-0-15V supply. You need 28V-0-28V.
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Old 1st July 2020, 04:26 PM   #1097
bajjisw is offline bajjisw  United States
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One or two ? If two, how are they wired ?
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Old 1st July 2020, 04:29 PM   #1098
Dennis Hui is offline Dennis Hui  Canada
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It looks consistent with setting 28V and getting +/-14V.

I think it's now time to pull out the transformer, caps and the
real power supply.
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Old 1st July 2020, 04:33 PM   #1099
Jim50hertz is offline Jim50hertz  United Kingdom
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OK, very noob mistake then!!! Oops.

I'm repurposing my Aleph J PSU, I've a new transformer. I build up the PSU and report back.
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Old 1st July 2020, 04:34 PM   #1100
Jim50hertz is offline Jim50hertz  United Kingdom
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Caps are rated 35v, is this OK?
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