This alpha 6 was my first amp that i ever bought a few years back and i thought i would do a recap witch i made a thread for.
I did see the the shape of the Mosfets where different on the right and it had signs of work done before. i thought it was just replaced and just looks different as sometimes they do.
Well i was wrong really wrong i took off the heatsinks and one channel was the original smf045 Mosfets (witch are not made anymore) and the right channel was the new replacements irf540 from STMicroelectronics.
i always thought the right channel sounded different i just thought i was going nuts 🤣
i was going to buy new ones for the left channel and then found out STMicroelectronics also no longer make the irf540 but some others do like Infineon and Vishay but there are all different specs.
STMicroelectronics irf540 HERE (Obsolete)
Infineon IRF540NPBF HERE (ACTIVE)
Infineon IRF540ZPBF HERE (ACTIVE)
Vishay IRF540PBF HERE (ACTIVE)
IXYS IXTP50N20P HERE (ACTIVE)
now the Vishay one looks the closest one but its Input Capacitance is nearly double and that's the same for all of them.
these are all what digikey says are possible replacements the IXYS being the odd one out, it has much higher drain and d to s voltage
so could u guys answer these questions for me
1. witch one would be the best replacement
2 .were could i get that thermal goop to replace the old stuff or do i just use that silicone pad stuff and if so where would i get that.
3. can i match theses in the same way i would a irfp240 with 12vdc and 100ohm resister like the firstwatt method
I'm also going to buy them in digikey's Manufacturers Standard Package to get a batch that will hopefully get me the best matching.
(i have not done matching before but i don't mind the extra cost to keep some spares around)
many thanks for any help.👍
I did see the the shape of the Mosfets where different on the right and it had signs of work done before. i thought it was just replaced and just looks different as sometimes they do.
Well i was wrong really wrong i took off the heatsinks and one channel was the original smf045 Mosfets (witch are not made anymore) and the right channel was the new replacements irf540 from STMicroelectronics.
i always thought the right channel sounded different i just thought i was going nuts 🤣
i was going to buy new ones for the left channel and then found out STMicroelectronics also no longer make the irf540 but some others do like Infineon and Vishay but there are all different specs.
STMicroelectronics irf540 HERE (Obsolete)
Infineon IRF540NPBF HERE (ACTIVE)
Infineon IRF540ZPBF HERE (ACTIVE)
Vishay IRF540PBF HERE (ACTIVE)
IXYS IXTP50N20P HERE (ACTIVE)
now the Vishay one looks the closest one but its Input Capacitance is nearly double and that's the same for all of them.
these are all what digikey says are possible replacements the IXYS being the odd one out, it has much higher drain and d to s voltage
so could u guys answer these questions for me
1. witch one would be the best replacement
2 .were could i get that thermal goop to replace the old stuff or do i just use that silicone pad stuff and if so where would i get that.
3. can i match theses in the same way i would a irfp240 with 12vdc and 100ohm resister like the firstwatt method
I'm also going to buy them in digikey's Manufacturers Standard Package to get a batch that will hopefully get me the best matching.
(i have not done matching before but i don't mind the extra cost to keep some spares around)
many thanks for any help.👍
Waht are the issues likely to be?
Increased capacitance limits slew rate?
Phase shift impacting stability?
Regarding heat sink compound, I've bought small tubes from ebay.
I used some no-name grey stuff, and it worked to keep the CPU of my PC cool, it tells me the junction temp, so I'm fairly confident it's OK for an amp.
If the package and heatsink are flat, plain silicone grease may be good enough?
You just want a really thin, but complete, coating.
Increased capacitance limits slew rate?
Phase shift impacting stability?
Regarding heat sink compound, I've bought small tubes from ebay.
I used some no-name grey stuff, and it worked to keep the CPU of my PC cool, it tells me the junction temp, so I'm fairly confident it's OK for an amp.
If the package and heatsink are flat, plain silicone grease may be good enough?
You just want a really thin, but complete, coating.
Silicone grease is much less good - use thermal paste and not too much! But normally there's a thermal pad anyway?
i did more digging and found the STMicroelectronics STP24NF10 Mosfet, it matches the irf540 and its cheaper then the Vishay lead free version and it has the same input capacitance 870pF (for context the vishay and the others had above 1700pF) , better Continuous Drain at 26A and with lower rds at 60mOhm
so I'm going to replace it with the STP24NF10 (also same package)
Here are the spec sheets
STMicroelectronics irf540 (HERE)
STMicroelectronics STP24NF10 (HERE)
(links are taken from Digi key witch i guess its to STMicroelectronics's site)
could someone that knows there stuff take a look at it and tell me if I'm right or not. (i haven't really got an idea what i should look for lol 🤣 )
thanks
so I'm going to replace it with the STP24NF10 (also same package)
Here are the spec sheets
STMicroelectronics irf540 (HERE)
STMicroelectronics STP24NF10 (HERE)
(links are taken from Digi key witch i guess its to STMicroelectronics's site)
could someone that knows there stuff take a look at it and tell me if I'm right or not. (i haven't really got an idea what i should look for lol 🤣 )
thanks
UPDATE:
i have replaced the old odd Mosfets with STMicroelectronics STP24NF10, left channel had smf045 and right had ST irf540
(the only thing i could see was the max rds on it was lower but the avg was the same)
the amp did not explode when i turned it on! 🤣
I did not match the Mosfets as i could not get my matching thing working so i gave up but they are most likely from the same batch and sounded fine through a woofer for testing.
i then replaced all the electrolytic capacitors except 2 witch are power side for the volume motor and remote control.
put it back together and set the IQ to 4mV after 5mins
now just to wait till i can plug in some speakers and test it out!
the one thing i hate about the alpha 6 that when i turn it on it draws the woofers in quite a bit, i mite have to install some kinda relay and protect circuit what do you think?
i have replaced the old odd Mosfets with STMicroelectronics STP24NF10, left channel had smf045 and right had ST irf540
(the only thing i could see was the max rds on it was lower but the avg was the same)
the amp did not explode when i turned it on! 🤣
I did not match the Mosfets as i could not get my matching thing working so i gave up but they are most likely from the same batch and sounded fine through a woofer for testing.
i then replaced all the electrolytic capacitors except 2 witch are power side for the volume motor and remote control.
put it back together and set the IQ to 4mV after 5mins
now just to wait till i can plug in some speakers and test it out!
the one thing i hate about the alpha 6 that when i turn it on it draws the woofers in quite a bit, i mite have to install some kinda relay and protect circuit what do you think?
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