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Old 22nd February 2010, 05:50 PM   #51
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Hi Helmuth,

Was is your experience with the changes proposed in the Belgian Service Paper. Did they give you any problems? What is your opinion on the fact thes were advised for safety purposes.
The lower bias values are not new to me.
I own quite a few v-fet amps and when this changes make sense I have to go through them once more.
And Yes great job and very entertaining and educational. And thanks for extra potential weak points you point to. Makes sense.
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Old 20th December 2012, 05:59 PM   #52
Helmuth is offline Helmuth  Netherlands
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Quote:
Originally Posted by roerdomp View Post
Hi Helmuth,

Was is your experience with the changes proposed in the Belgian Service Paper. Did they give you any problems? What is your opinion on the fact thes were advised for safety purposes.
The lower bias values are not new to me.
I own quite a few v-fet amps and when this changes make sense I have to go through them once more.
And Yes great job and very entertaining and educational. And thanks for extra potential weak points you point to. Makes sense.
The repaired end stage blew a year after the repair I did turn up the bias higher then the belgium paper.

I think this is the cause of the failure. I would advise to follow the advise.

Also the chinese nos Vfet could be the cause I have al ready a new set that I have to install.
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Old 20th December 2012, 06:05 PM   #53
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what is the current situation with the VFETs from the output stage availability, still crazy prices? i got offerred one of these but all the output transistors were exchanged for some crap so it would need a full restoration.
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Old 20th December 2012, 06:18 PM   #54
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Thanks Helmuth... I have used some ranking 52/53 v-fets for my TA-N7b... they work fine!
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Old 20th December 2012, 06:19 PM   #55
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Hi Anubisgrau,

Not much available at all... some and yes crazy prices aswell. But you try the ones offered via ebay
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Old 2nd December 2013, 06:38 AM   #56
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Old 3rd January 2014, 07:20 PM   #57
jlithen is offline jlithen  Finland
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Default 2SK60 rank 55

I'm going to repair a Wega VFET amp I just bought and I already ordered two 2SK60 rank 55.
I do not have the amp yet so I don't know if I even need to replace the VFETs.
Doesn't hurt to have a few spare ones though

I did some testing with 32V between D and S.
To get the current down to 30mA I needed to apply 12V between G and S on one VFET and 17V on the other.

This cannot be right or what do you think?
They should probably be within a few hundred mV if they are the same rank.
Paralleling these must be impossible!?

Same ebay seller offers rank 33 2SJ18...I would like to measure one
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Old 29th January 2014, 08:27 PM   #58
jlithen is offline jlithen  Finland
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Got a pair of 2SJ18 from Jims and same thing.
One is perfect and the other has a Vgs of like 23V.
Jims was anyway helpful and promised to replace it for me.
The chinese seller I got the K60 from had to get negative feedback.
He was useless

Wonder what the rank 33 devices are??? Many chinese sellers have them.
I got some J28 K82 today, they might work too.

Anyway I got my amp and it was working, but one channel was very weak.
Turned out the weak channel had shorted VFETS, all of them.

I did the diode change (loosely matched) and a total recap of the PA board.
The PS board is not yet totally recapped and some caps are SAMXON.
I hate Samwha and samxon and all other crappy caps, will replace all with Panasonic FC when I get them.
The ones in the signal path I may try to replace with something even better

Anyway I have the same drive voltage issue as many others here.
No blown trace on cap board.
I will check connections, but I think those are wrapped in mine too and not with a connector.
Interesting is that the amp was working, so PSU section cannot be totally faulty
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Old 29th January 2014, 11:51 PM   #59
Junm is offline Junm  Philippines
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Quote:
Originally Posted by jlithen View Post
I'm going to repair a Wega VFET amp I just bought and I already ordered two 2SK60 rank 55.
I do not have the amp yet so I don't know if I even need to replace the VFETs.
Doesn't hurt to have a few spare ones though

I did some testing with 32V between D and S.
To get the current down to 30mA I needed to apply 12V between G and S on one VFET and 17V on the other.

This cannot be right or what do you think?
They should probably be within a few hundred mV if they are the same rank.
Paralleling these must be impossible!?

Same ebay seller offers rank 33 2SJ18...I would like to measure one
As per other members JUMA, ILIMZN and Nmos57 and even Mr. Pass, V-fets should be matched, see some discussion here What to do with this Sony V-FETS?

How did you measure your VFets , do you have a schematics and can you share it with me. I want to do it since I also have 2SK60 rank 54 and J18 ranks 57.. i want to try the designs posted in that thead and matched the devices for parallel mode.

Thanks
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Old 30th January 2014, 09:28 AM   #60
jlithen is offline jlithen  Finland
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Thanks for the link to the other thread.
I did not see that one before. It sure has lots of useful info!

I have a 2x32V Thurlby Thandar powersupply (very good PSU, can recommend)

I set the two outputs in series and the one over drain and source to 32V 500mA
Then I measured voltage drop at VGS=0 (usually around half a volt)
Then the IDS=0 voltage, usually around 10V for good devices, 20V for chinese ones
Then IDS 40mA (just a value I thought about using for some reason) This was usually like a volt lower than the previous value.

From the TA-5650 schematic it was easy to figure out how the voltages should be connected.

Which schematic do you need?
The amp schematic can be found at hifiengine and other schematics I do not have.
I will sure send the one I have if you like?
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