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Sony Vfet Illustrated build guide
Sony Vfet Illustrated build guide
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Old 5th November 2017, 01:27 PM   #341
stijn001 is offline stijn001  Netherlands
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Sony Vfet Illustrated build guide
I’ve started Bias’ing up the front end & am not getting up to 1.5V across R5/R6 on both channels, one channel reaches 1.24V and the other 1.3V (after warmup) with one of the P3 or P4 pots fully clockwise on the channels.

How would you suggest I solve this, do I increase R5/R6 and with how much or swap-out the P3/P4 for 1KOhm pots?

Also I still measure a high supply voltage 31V between G-T6&T8 and T3&T5 measure 21.4V. Are these acceptable?
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Old 5th November 2017, 01:37 PM   #342
Rodeodave is offline Rodeodave  Austria
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What FETs are you using for Q5 and Q6? What value are P3 and P4 currently?

Toshiba 2SJ313/2SK2013 want about 2V Vgs to turn on, which you can reach with 500R P3/P4.

Fairchild FQP3P20/FQP3N30 want about 4V to turn on, which requires 1k P3/P4.
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Old 5th November 2017, 03:10 PM   #343
WalterW is offline WalterW  Netherlands
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Sony Vfet Illustrated build guide
Increase R34 and R35 a bit, double the 221 resistors to 470 Ohm or 560 Ohm.
The other measurements look all OK, because you are still not serious loading the PSU with only the frontend biased up.
The voltages will get lower when the VFET's are getting their bias.
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Old 5th November 2017, 05:25 PM   #344
stijn001 is offline stijn001  Netherlands
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Thanks Dave and Walter,

One of the P3/P4 pairs is at 473/463 Ohm's, the P3 being as far as it will go. I'm using the Fairchild FQP3P20/FQP3N30's. Since I can't get the 1x turn pots dialed in accurately either, the tiniest adjustment would still offset the bias by 1V, I've gone ahead and ordered some 4 turn pots and some higher value Dales to replace R5/R6 (which I hadn't lying around).
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Old 10th November 2017, 08:16 PM   #345
manniraj is offline manniraj  India
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Quote:
Originally Posted by manniraj View Post
Yes it did not change started at around 22v and remained the same with any turns of P3/P4. Hence as you said the FQP20 might have gone or may be both FQN20 as well.
I changed the suspected P3 trimmer to a new 500R single turn one and also replaced R34/35 with 1K ohm. Still I am not able to get any voltage across T6-7 with the P3 trimmer turning. Now the last resort is that I need to replace the FQP20/N20 mosfets which I have ordered from element14 and might take another 10 days to arrive.
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Old 11th November 2017, 07:39 AM   #346
manniraj is offline manniraj  India
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After the P3 pot change the below are the test voltages:

G-T6 = +32V G-T8 = -32V
G-T4 = -23.7V G-T2 = +23.8V
T6-T7 = 0V T8-T9 = 0.232V
T6-T11 = 11.95V T8-T13 = 11.62V
G-T18 = -31.8V (seems to be a issue)
G-T14 = +15.3V G-T15 = -15.3V
G-T19 = +13.4V G-T20 = -12.3V
G-T17 = -21.2V (seems to be issue) G-T16 = 5.6V

The above values with P34/35 with 1K ohm and the P1/2 at the center position, no other changes. Also I checked for continuity of the FQP20/N20 mosfets and I get good amount of resistance on the DMM for both and does not seem to be any issue. Based on the above values like the G-T18 and G-T17 being abnormal values compared to the optimal values as per the guide any suggestion was could be the problem as I have cross checked for any loose soldering/connection as well as the wrong resistance values and everything seems to be correctly placed and also the orientation.

Thanks
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Old 11th November 2017, 09:35 AM   #347
Rodeodave is offline Rodeodave  Austria
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How about you post well lit, in-focus pictures with good resolution of both the top and bottom side showng all of the pcbs and psu? Maybe there's something we can spot.
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Old 11th November 2017, 09:42 AM   #348
metallicus69 is offline metallicus69  Netherlands
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T6-T10? T8-T12? Do you have enough voltage on the grids of Q5 Q6?
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Old 11th November 2017, 09:45 AM   #349
metallicus69 is offline metallicus69  Netherlands
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Even better, T9-T12 and T7-T10? Measure on the transistors legs directly please
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Old 11th November 2017, 09:53 AM   #350
manniraj is offline manniraj  India
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Originally Posted by Rodeodave View Post
How about you post well lit, in-focus pictures with good resolution of both the top and bottom side showng all of the pcbs and psu? Maybe there's something we can spot.
Here are the close up pics of the top and bottom of the PCB board.

Sony VFET2 - Album

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Thanks

Last edited by manniraj; 11th November 2017 at 10:02 AM.
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