What mosfets to use?

seafire · 23rd March 2009, 02:24 PM

I have blown mosfet 2SK405 paired with 2SJ115.i cant find the originals and have been told to use 2SK1529 / 2SJ200.The units I can get are real Toshiba jobs.So come all you electronics wizards throw me a ******* bone here and do the cross check for me and advice

I have the data sheets but dont really know what to look for

These are for a Marantz PM 94 AMP.How much will the newer fets affect my bias ??
Waiting for a wizard

Seafire

AndrewT · 23rd March 2009, 02:44 PM

compare
conductance Yfs (5S)
Ciss, Coss (900pF, 180pF)
Vgs off (0.8V to 2.8V)
Vdss (200V)
Id (12A)
Pd (150W)
package (To3p= To247)
Pin allocation (GDS D connected to thermal face)

2sk1530 data shown in parenthesis ().

The bias depends very much on the Vgs of each of the devices. This varies enormously for all FETs, whether jFETs, or Lfets, or Vfets.
Changing any FET virtually guarantees that you will have a different Vgs and this in turn guarantees that you will have to adjust the bias back to specification.

seafire · 23rd March 2009, 03:33 PM

Hi thank you for the response however could you be a little more specific..I did not really understand the reply you sent me

Is this the specs for the newer fets and are they ok to use ore what suggestions thanking you in advance

AndrewT · 23rd March 2009, 05:20 PM

those were the specs for the 1530.
I don't have your old ones to compare.

You said you have the datasheets.
Now compare.

Lumba Ogir · 24th March 2009, 11:01 AM

seafire,
the main difference is higher Gm for 2SK1529, which means higher capacitances.

seafire · 24th March 2009, 02:01 PM

hmmm is this a good or a bad thing in terms of sound quality ie. to preserve the sweet musical quality of this amp

Lumba Ogir · 24th March 2009, 03:18 PM

seafire,
you are a painstaking person, which I don`t dislike. Well, if you ask me, I`d say it`s a step backwards. For 2SK405, Crss is 60pF specified at Vds 10, while for 2SK1529 it is 90pF at Vds 30 (capacitances decrease with increasing voltages). Hitachi went in the opposite direction in the case of 2SK2220, impressing me greatly.

foo · 24th March 2009, 03:27 PM

If cost is not a problem, you can simply go for Magnatec MOSFETs.
They are identical to Sk134 SJ49 and with better spec.

Lumba Ogir · 24th March 2009, 03:32 PM

foo,

Quote:

They are identical to Sk134 SJ49 and with better spec.

In what regard?

AndrewT · 24th March 2009, 03:39 PM

Does he need Vfets or Lfets?
The 2sk1530/j160 are Vfets with very low Vgs.

The Magnatec /SK134/SK1058 are Lfets.

23rd March 2009, 02:24 PM	#1
seafire diyAudio Member Join Date: Feb 2009	What mosfets to use? I have blown mosfet 2SK405 paired with 2SJ115.i cant find the originals and have been told to use 2SK1529 / 2SJ200.The units I can get are real Toshiba jobs.So come all you electronics wizards throw me a ******* bone here and do the cross check for me and advice I have the data sheets but dont really know what to look for These are for a Marantz PM 94 AMP.How much will the newer fets affect my bias ?? Waiting for a wizard Seafire

23rd March 2009, 02:44 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	compare conductance Yfs (5S) Ciss, Coss (900pF, 180pF) Vgs off (0.8V to 2.8V) Vdss (200V) Id (12A) Pd (150W) package (To3p= To247) Pin allocation (GDS D connected to thermal face) 2sk1530 data shown in parenthesis (). The bias depends very much on the Vgs of each of the devices. This varies enormously for all FETs, whether jFETs, or Lfets, or Vfets. Changing any FET virtually guarantees that you will have a different Vgs and this in turn guarantees that you will have to adjust the bias back to specification. __________________ regards Andrew T.

23rd March 2009, 05:20 PM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	those were the specs for the 1530. I don't have your old ones to compare. You said you have the datasheets. Now compare. __________________ regards Andrew T.

24th March 2009, 03:39 PM	#10
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Does he need Vfets or Lfets? The 2sk1530/j160 are Vfets with very low Vgs. The Magnatec /SK134/SK1058 are Lfets. __________________ regards Andrew T.

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23rd March 2009, 03:33 PM	#3
seafire diyAudio Member Join Date: Feb 2009	Hi thank you for the response however could you be a little more specific..I did not really understand the reply you sent me Is this the specs for the newer fets and are they ok to use ore what suggestions thanking you in advance

24th March 2009, 11:01 AM	#5
Lumba Ogir Banned Join Date: Apr 2005 Location: Stockholm	seafire, the main difference is higher Gm for 2SK1529, which means higher capacitances.

24th March 2009, 02:01 PM	#6
seafire diyAudio Member Join Date: Feb 2009	hmmm is this a good or a bad thing in terms of sound quality ie. to preserve the sweet musical quality of this amp

24th March 2009, 03:18 PM	#7
Lumba Ogir Banned Join Date: Apr 2005 Location: Stockholm	seafire, you are a painstaking person, which I don`t dislike. Well, if you ask me, I`d say it`s a step backwards. For 2SK405, Crss is 60pF specified at Vds 10, while for 2SK1529 it is 90pF at Vds 30 (capacitances decrease with increasing voltages). Hitachi went in the opposite direction in the case of 2SK2220, impressing me greatly.

24th March 2009, 03:27 PM	#8
foo diyAudio Member Join Date: May 2004 Location: ...	If cost is not a problem, you can simply go for Magnatec MOSFETs. They are identical to Sk134 SJ49 and with better spec.

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