fet help please 2SK135

SA-12 · 2nd March 2009, 03:22 AM

Ok so I am going to try the mosfet power supply mod to a scrap Dynaco st120. I know the amp is more or less garbage but it is cheap and fun to work with. I have tried many times with this power supply upgrade but keep falling short on regulated voltage. I have checked and re-checked a dozen times the circuit and have found small errors and fixed. My voltage is to low, about 58v on cap 12 when I should have about 70v or so. The control zenner is fine but I changed it just to be sure a couple times. I have also changed the FET a couple times with the same result. This is what I have that is not working, any advice would be nice. I am having problems finding a sub for a 2SK135 and that is why I used the IRF241 and it has a nice TO3 case that I like.

FET used IRF241 which should work right?
Now I admit I cheeped out on the rectifiers and used NTE components, could this be a cause?. They are NTE588 a 200v/3a ultra fast and should work perfect.

I think my entire problem lies with the FET being used which on paper should fit nice but in reality is not giving me the regulated voltage I need.

SA-12 · 2nd March 2009, 03:54 AM

I know I could use 2sk1057 but as stated I wanted to maintain the original TO3 case style. If any member here have some experience building this design and can offer some advise that would be greatly welcome. Thanks all.

woody · 2nd March 2009, 05:45 AM

Sure would help if you posted the circuite.

SA-12 · 2nd March 2009, 02:23 PM

SA-12 · 2nd March 2009, 02:26 PM

there ya go, very simple but get it to work right

SA-12 · 2nd March 2009, 02:33 PM

fyi cap 12 3300uf@100v
cap 9 and 11 500uf@100v and 1000uf@100v
diode 4,5,7,8, 200prv@3amp.
cap 16 .01@1kv.

I have this supply built exactly like the one in the pic, I have built it many times the exact same way and have never reached anything over 60v on cap 12.

Tube_Dude · 2nd March 2009, 11:02 PM

Hi

If memory serves, the IRF241 have not the same pin out of the 2SK135...

SA-12 · 2nd March 2009, 11:49 PM

yeah, figured that out with destroyed fet number one

, I think I have pinout right. I downloaded the spec for this fet and pinout was clearly shown. I had it wrong at first. When i had pins reversed I was getting 98vdc on cap 12.

Tube_Dude · 2nd March 2009, 11:58 PM

Quote:

Originally posted by SA-12
yeah, figured that out with destroyed fet number one , I think I have pinout right. I downloaded the spec for this fet and pinout was clearly shown. I had it wrong at first. When i had pins reversed I was getting 98vdc on cap 12.

In the 2SK135 the case is the source, In the IRF the case is the drain...

SA-12 · 3rd March 2009, 12:07 AM

ok so turns out the first way I had it was right, and I got 98v on cap 12, zenner is good. 1n4760. what am I doing wrong

2nd March 2009, 03:22 AM	#1
SA-12 diyAudio Member Join Date: Jan 2009	fet help please 2SK135 Ok so I am going to try the mosfet power supply mod to a scrap Dynaco st120. I know the amp is more or less garbage but it is cheap and fun to work with. I have tried many times with this power supply upgrade but keep falling short on regulated voltage. I have checked and re-checked a dozen times the circuit and have found small errors and fixed. My voltage is to low, about 58v on cap 12 when I should have about 70v or so. The control zenner is fine but I changed it just to be sure a couple times. I have also changed the FET a couple times with the same result. This is what I have that is not working, any advice would be nice. I am having problems finding a sub for a 2SK135 and that is why I used the IRF241 and it has a nice TO3 case that I like. FET used IRF241 which should work right? Now I admit I cheeped out on the rectifiers and used NTE components, could this be a cause?. They are NTE588 a 200v/3a ultra fast and should work perfect. I think my entire problem lies with the FET being used which on paper should fit nice but in reality is not giving me the regulated voltage I need.

2nd March 2009, 11:02 PM	#7
Tube_Dude diyAudio Member Join Date: Mar 2002 Location: Aveiro-Portugal	Hi If memory serves, the IRF241 have not the same pin out of the 2SK135... __________________ Jorge

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2nd March 2009, 03:54 AM	#2
SA-12 diyAudio Member Join Date: Jan 2009	I know I could use 2sk1057 but as stated I wanted to maintain the original TO3 case style. If any member here have some experience building this design and can offer some advise that would be greatly welcome. Thanks all.

2nd March 2009, 05:45 AM	#3
woody diyAudio Member Join Date: Jan 2002 Location: Tyrone Ga. U.S.A.	Sure would help if you posted the circuite.

2nd March 2009, 02:23 PM	#4
SA-12 diyAudio Member Join Date: Jan 2009

2nd March 2009, 02:26 PM	#5
SA-12 diyAudio Member Join Date: Jan 2009	there ya go, very simple but get it to work right

2nd March 2009, 02:33 PM	#6
SA-12 diyAudio Member Join Date: Jan 2009	fyi cap 12 3300uf@100v cap 9 and 11 500uf@100v and 1000uf@100v diode 4,5,7,8, 200prv@3amp. cap 16 .01@1kv. I have this supply built exactly like the one in the pic, I have built it many times the exact same way and have never reached anything over 60v on cap 12.

2nd March 2009, 11:49 PM	#8
SA-12 diyAudio Member Join Date: Jan 2009	yeah, figured that out with destroyed fet number one , I think I have pinout right. I downloaded the spec for this fet and pinout was clearly shown. I had it wrong at first. When i had pins reversed I was getting 98vdc on cap 12.

3rd March 2009, 12:07 AM	#10
SA-12 diyAudio Member Join Date: Jan 2009	ok so turns out the first way I had it was right, and I got 98v on cap 12, zenner is good. 1n4760. what am I doing wrong

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