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.
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.
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.
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.
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.
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.
, 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.
SA-12 said:yeah, figured that out with destroyed fet number one
In the 2SK135 the case is the source, In the IRF the case is the drain... 😉
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
SA-12 said: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
The Mosfet is shorted (burned)... 😉
I thought so too, but it is not. I had five of these fets can they all be shorted. It is not a overvoltage issue thats for sure. I got 2 left, will try again I guess. 😡
unless these fets are super sensitive to heat and static. I do ground myself before touching them, but I also solder direct to the pins. They have a huge pin, twice the size of normal pins on say a 2n3772.
Inspect again the pins layout.
The pins position is the same of this one:
http://pdf1.alldatasheet.com/datasheet-pdf/view/67474/INTERSIL/IRF244.html
The pins position is the same of this one:
http://pdf1.alldatasheet.com/datasheet-pdf/view/67474/INTERSIL/IRF244.html
yep that the pinout I used all along, still get 98v on cap 12. I have to check some other component values but I am sure it is all right. I might have to make my own pcb as I just can't trust the original pcb even though I checked it now about 5-6 times to make sure I got it right. To many traces not being used it is a little confusing.
I thought I would remove the original caps from circuit and aligator clip some newer versions in still no difference. 98v cap 12. what could cause the high voltage?, a zenner right well checked and re-checked and replaced for the heck of it😀
it is funny because some of the kits I have built and amps i have worked on without problems, then this exceedingly simple circuit I can't get right. I have been trying this off and on for the past couple years, it is my shame.😡
going to hook up again tomorrow, keep following the thread please and i will report back. thanks for your help
- Status
- Not open for further replies.