Best replacement transistors for this amp?

nitroboy · 26th May 2010, 03:38 PM

Hi
I hope this isn't a problem that I borrow your threat.
I was hoping that someone could tell me what would be the best transistor(mosfet) for my amplifier. It's an car amp and ia has 200W on 4 speakers. A friend gave it to me becouse he broke it. I've found the problem (a trasistor was blown). and i want to know what would be the best replacement or even better how much stronger could I make it.

thanks

Jon Lord · 05:43 PM

The transistors on your first picture are Bipolars (not MOSFETs) and they are fakes (no name, Chinese crap ... so this is the reason of failure).

You can't really use a different transistor than the current type, otherwise the bias current would be different and it doesn't seem to be adjustable.
One powerful alternative could be e.g. 2STA2120 and 2STC5948, but I doubt that replacing the bad transistors will really help, because certainly other devices are damaged.

nitroboy · 26th May 2010, 05:42 PM

I already know that

... I want to know what would be an replacement and if I could make it stronger...
and their all the same. Only two were replaced I think becouse there were marks on the pcb. but they their names scraped off.

sorry for my english...

Jon Lord · 26th May 2010, 05:55 PM

nitroboy:

I'm confused, are these 2SB and 2SD types the originals or not ? They aren't isn't it !!

Regarding the general question of this thread, did someone ever try the following MOSFET pair:

FQA36P15
FQA46N15 from Fairchild

These seem to be rather powerful and robust VMOS (planar stripe) type, which are damn cheap, low Crss and can dissipate at least 250W.

They already worked in a prototype of mine, but I never qualified them any further (measurement and listening wise).

richie00boy · 26th May 2010, 05:57 PM

You cannot make it stronger because the extra heat is a problem and also the power supply is not big enough.

Try to find the correct parts or similar good quality ones.

nitroboy · 06:33 PM

I have to replace them anyways so... but don't I have to worry that the pcb could be dameged when the transistor let's trough more amps ?
yes they are original the one on the photo isn't

26th May 2010, 05:38 PM	#2
Jon Lord diyAudio Member Join Date: May 2005 Location: Kaiserslautern	The transistors on your first picture are Bipolars (not MOSFETs) and they are fakes (no name, Chinese crap ... so this is the reason of failure). You can't really use a different transistor than the current type, otherwise the bias current would be different and it doesn't seem to be adjustable. One powerful alternative could be e.g. 2STA2120 and 2STC5948, but I doubt that replacing the bad transistors will really help, because certainly other devices are damaged. __________________ My amplifier is very musical: It accompanies myself on the grand piano, that's not half bad ! Last edited by Jon Lord; 26th May 2010 at 05:43 PM.

26th May 2010, 05:55 PM	#4
Jon Lord diyAudio Member Join Date: May 2005 Location: Kaiserslautern	nitroboy: I'm confused, are these 2SB and 2SD types the originals or not ? They aren't isn't it !! Regarding the general question of this thread, did someone ever try the following MOSFET pair: FQA36P15 FQA46N15 from Fairchild These seem to be rather powerful and robust VMOS (planar stripe) type, which are damn cheap, low Crss and can dissipate at least 250W. They already worked in a prototype of mine, but I never qualified them any further (measurement and listening wise). __________________ My amplifier is very musical: It accompanies myself on the grand piano, that's not half bad !

26th May 2010, 05:57 PM	#5
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	You cannot make it stronger because the extra heat is a problem and also the power supply is not big enough. Try to find the correct parts or similar good quality ones. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

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26th May 2010, 05:42 PM	#3
nitroboy diyAudio Member Join Date: Feb 2010	I already know that ... I want to know what would be an replacement and if I could make it stronger... and their all the same. Only two were replaced I think becouse there were marks on the pcb. but they their names scraped off. sorry for my english...

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