50 Watt Amp Final Transistors


George Korper
 

Hi,
I need a trusted source and part number with link for the best replacement 
IRF 510 finals. 
Thanks,
George


Hans Summers
 

Hi George 

I tested 6 different supplier IRF510 before choosing the one used in the QRP Labs kits. It's not one you will be able to buy in single quantities without going through all that extensive testing again. I think you should just get the Digikey IRF510 made by Vishay, Digikey part number IRF510PBF-ND, I'm sure it will be fine. 

73 Hans G0UPL 

On Sat, Feb 29, 2020, 20:28 George Korper <georgekorper@...> wrote:
Hi,
I need a trusted source and part number with link for the best replacement 
IRF 510 finals. 
Thanks,
George


George Korper
 

Thank you;

will do!


On Sat, Feb 29, 2020, 12:26 PM Hans Summers <hans.summers@...> wrote:
Hi George 

I tested 6 different supplier IRF510 before choosing the one used in the QRP Labs kits. It's not one you will be able to buy in single quantities without going through all that extensive testing again. I think you should just get the Digikey IRF510 made by Vishay, Digikey part number IRF510PBF-ND, I'm sure it will be fine. 

73 Hans G0UPL 

On Sat, Feb 29, 2020, 20:28 George Korper <georgekorper@...> wrote:
Hi,
I need a trusted source and part number with link for the best replacement 
IRF 510 finals. 
Thanks,
George


K2DB Paul Mackanos
 

Hans, why don't you just add it under components in your shops ?


On Sat, Feb 29, 2020, 1:26 PM Hans Summers <hans.summers@...> wrote:
Hi George 

I tested 6 different supplier IRF510 before choosing the one used in the QRP Labs kits. It's not one you will be able to buy in single quantities without going through all that extensive testing again. I think you should just get the Digikey IRF510 made by Vishay, Digikey part number IRF510PBF-ND, I'm sure it will be fine. 

73 Hans G0UPL 

On Sat, Feb 29, 2020, 20:28 George Korper <georgekorper@...> wrote:
Hi,
I need a trusted source and part number with link for the best replacement 
IRF 510 finals. 
Thanks,
George


Hans Summers
 

Hi Paul

Most of the parts for the QRP Labs kits, I buy the correct amount for the number of kits, based on the number of PCBs made. If I buy a lot extra to be able to offer spares, it would increase the costs, logistics problems and the admin headaches... producing kits is already hard enough without multiplying it all by offering all the components too... all the components used in QRP Labs kits are generally easy to find, here aren't any difficult to find components... the theory goes that if people need spares they should be quite easy to find.

73 Hans G0UPL 

On Sat, Feb 29, 2020, 21:55 K2DB Paul Mackanos <paul.mackanos@...> wrote:
Hans, why don't you just add it under components in your shops ?

On Sat, Feb 29, 2020, 1:26 PM Hans Summers <hans.summers@...> wrote:
Hi George 

I tested 6 different supplier IRF510 before choosing the one used in the QRP Labs kits. It's not one you will be able to buy in single quantities without going through all that extensive testing again. I think you should just get the Digikey IRF510 made by Vishay, Digikey part number IRF510PBF-ND, I'm sure it will be fine. 

73 Hans G0UPL 

On Sat, Feb 29, 2020, 20:28 George Korper <georgekorper@...> wrote:
Hi,
I need a trusted source and part number with link for the best replacement 
IRF 510 finals. 
Thanks,
George


Adam <adam.haynes1@...>
 

Hi George,
What Hans said.
I bought a bunch and they work great.
https://au.rs-online.com/web/p/mosfets/9190023/


ajparent1/KB1GMX
 

IRF510 from any source not Ebay or other random sources.

Typically  I use Digikey and Mouser, Allied,  and Jameco with zero issues.
Another is RFparts.com,  the real McCoy at real prices.

The problem with any RF device and a long list of them common to ham
and hobby use is buy cheap, get cheap counterfeits.  I buy them from known
sources usually at higher (fair) prices I get what I wanted and quality or at
least a firm I can actually go back to.

The beauty of IRF510 is typical price is well under 1.25$ each from reputable sources.
and at last buy a few weeks ago I got 10 for 88 cents each (VIshay IRF510).


Allison
-------------------------------
Please reply on list so we can share.
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George Korper
 

Hi Allison,
I had a good amp that needed new
Finals. 20 meters.

 I ordered on Amazon. Put in replacements. No data, looked kind of cheap, etc.

Checked bias using current limiting supply. All ok. Pot is barely above anti clockwise 

Left practice mode. Output at 12 volts 10 watts as I raised voltage it seemed low output. At 20 volts it was working but I started to hear a ripple develop.  20 watts output for 10 seconds. This was half the output of the supplied transistors.

Then they blew and supply tripped out. 

Is this behavior consistent with poor quality mosfets?

On Sat, Feb 29, 2020, 2:48 PM ajparent1/KB1GMX <kb1gmx@...> wrote:
IRF510 from any source not Ebay or other random sources.

Typically  I use Digikey and Mouser, Allied,  and Jameco with zero issues.
Another is RFparts.com,  the real McCoy at real prices.

The problem with any RF device and a long list of them common to ham
and hobby use is buy cheap, get cheap counterfeits.  I buy them from known
sources usually at higher (fair) prices I get what I wanted and quality or at
least a firm I can actually go back to.

The beauty of IRF510 is typical price is well under 1.25$ each from reputable sources.
and at last buy a few weeks ago I got 10 for 88 cents each (VIshay IRF510).


Allison
-------------------------------
Please reply on list so we can share.
No direct email, it goes to bit bucket due address harvesting in groups.IO


George Korper
 

BTW just ordered from Digikey.


On Sat, Feb 29, 2020, 2:48 PM ajparent1/KB1GMX <kb1gmx@...> wrote:
IRF510 from any source not Ebay or other random sources.

Typically  I use Digikey and Mouser, Allied,  and Jameco with zero issues.
Another is RFparts.com,  the real McCoy at real prices.

The problem with any RF device and a long list of them common to ham
and hobby use is buy cheap, get cheap counterfeits.  I buy them from known
sources usually at higher (fair) prices I get what I wanted and quality or at
least a firm I can actually go back to.

The beauty of IRF510 is typical price is well under 1.25$ each from reputable sources.
and at last buy a few weeks ago I got 10 for 88 cents each (VIshay IRF510).


Allison
-------------------------------
Please reply on list so we can share.
No direct email, it goes to bit bucket due address harvesting in groups.IO


George Korper
 

Allison and Others,
Anyone have any tips on a way to install the finals on a temporary basis to avoid
ruining the board? That way if i have some other mistake which blows the finals
I could save a lot of grief and perhaps the rest of my work!
George

On Sat, Feb 29, 2020 at 5:04 PM George Korper via Groups.Io <georgekorper=gmail.com@groups.io> wrote:
BTW just ordered from Digikey.

On Sat, Feb 29, 2020, 2:48 PM ajparent1/KB1GMX <kb1gmx@...> wrote:
IRF510 from any source not Ebay or other random sources.

Typically  I use Digikey and Mouser, Allied,  and Jameco with zero issues.
Another is RFparts.com,  the real McCoy at real prices.

The problem with any RF device and a long list of them common to ham
and hobby use is buy cheap, get cheap counterfeits.  I buy them from known
sources usually at higher (fair) prices I get what I wanted and quality or at
least a firm I can actually go back to.

The beauty of IRF510 is typical price is well under 1.25$ each from reputable sources.
and at last buy a few weeks ago I got 10 for 88 cents each (VIshay IRF510).


Allison
-------------------------------
Please reply on list so we can share.
No direct email, it goes to bit bucket due address harvesting in groups.IO


ajparent1/KB1GMX
 

No, none as adding lead length via sockets is a bad thing.

With popper care board damage should  not happen.

Hint if you destroy them,  disassemble, cut the leads at
the package,  (they are dead!) and extract the leads one
at a time with a sufficiently hot iron and tweezer.

Clear the holes by heating the solder and using inertia
(sudden stop while molten) should clear the hole.

Do not drill or use pins or try to poke the tip of the iron in.
That often does more damage.

Allison
-------------------------------
Please reply on list so we can share.
No direct email, it goes to bit bucket due address harvesting in groups.IO


George Korper
 

THANK YOU ALLISON.  I tried your technique and you know what? 
You saved me from a great deal of grief! Again, I will just say, THANK YOU ALLISON!!!



On Sat, Feb 29, 2020 at 6:27 PM ajparent1/KB1GMX <kb1gmx@...> wrote:
No, none as adding lead length via sockets is a bad thing.

With popper care board damage should  not happen.

Hint if you destroy them,  disassemble, cut the leads at
the package,  (they are dead!) and extract the leads one
at a time with a sufficiently hot iron and tweezer.

Clear the holes by heating the solder and using inertia
(sudden stop while molten) should clear the hole.

Do not drill or use pins or try to poke the tip of the iron in.
That often does more damage.

Allison
-------------------------------
Please reply on list so we can share.
No direct email, it goes to bit bucket due address harvesting in groups.IO


George Korper
 

THANK YOU HANS,
The paragraph in the 50 PA on heat and is excellent. 
I was waiting for the right  Finals from Digikey, so I tried two different sets
IRF 510's  from Amazon. I can't believe how fast they heat up. What I don't understand
is why. What is wrong inside them? I am saying thank you because, it gave me a small taste of what
your experimenting is like. Buddy, you've got persistence. 

On Sun, Mar 1, 2020 at 11:37 AM George Korper <georgekorper@...> wrote:
THANK YOU ALLISON.  I tried your technique and you know what? 
You saved me from a great deal of grief! Again, I will just say, THANK YOU ALLISON!!!



On Sat, Feb 29, 2020 at 6:27 PM ajparent1/KB1GMX <kb1gmx@...> wrote:
No, none as adding lead length via sockets is a bad thing.

With popper care board damage should  not happen.

Hint if you destroy them,  disassemble, cut the leads at
the package,  (they are dead!) and extract the leads one
at a time with a sufficiently hot iron and tweezer.

Clear the holes by heating the solder and using inertia
(sudden stop while molten) should clear the hole.

Do not drill or use pins or try to poke the tip of the iron in.
That often does more damage.

Allison
-------------------------------
Please reply on list so we can share.
No direct email, it goes to bit bucket due address harvesting in groups.IO


ajparent1/KB1GMX
 

Amazon as a source is generally ok.

But the actual supplier is often a Ebay site and may be suspect.
One would think at the typically low prices for the IRF510 forgeries 
would be not worth it, but apparently it is real issue.  

Also VIshay and other have SIRF510 which is the same device
but the pin out is different, the drain and source reverse and the tab 
is source (grounded).  If put in a IRF510 spot they will immediately
heat up, maybe explode.  Reason there is a parasitic diode in
MOSFETS becaus eof the silicon and will look like a diode across
the power supply is subjected to wrong polarity. This kind of odd
pin out of parts is not  uncommon but unless clued it it will be
a unpleasant surprise..

They could also be off spec parts (formerly known as floor sweepings)
or that lot of parts has a very low Vgth (gate threshold voltage)
requiring a lower bias setting.   

I'd add this time of year ESD (carpet sparks) will kill most mosFETs.
That would show in a tester as unaccaprtable gate leakage or
outright dead.  In a circuit as an immediate fail on power up.

You did zero the setting first and reset for that pair?

Most if not all MOSfets are not drop in and require setting
the bias for the given devices in use.   THat applies to the
expensive RF Power LD-MOSFETS (the 200$ plus devices)
as well.

Also do not under any circumstances try to operate without
heat sinks mounted.

Allison
-------------------------------
Please reply on list so we can share.
No direct email, it goes to bit bucket due address harvesting in groups.IO


Hans Summers
 

HI George 

Yeah a large number of IRF510s and other MOSFET types perished during my R&D work... some quietly, some very loudly like a gun.

They get hot fast because they are dissipating a LOT of power as heat! So say the thermal resistance from IRF510 to heatsink is 3.5C/Watt and you're dissipating 20W per device, then the temperature rise will be 70C (on top of the current heatsink temperature). Being a relatively small device, their heat capacity is relatively small and so the temperature rise is quite rapid. 

Do NOT sit on the key! Use the amp as for normal CW type of duty cycle and everything will be fine. Normal CW is something around 50% duty cycle on average. 

You want to tune up your antenna? So you want to sit on the key while you make your adjustments? No! You shouldn't be doing that at full power anyway! Tune up at much lower power. 

During all my development I operated sensibly. In an hour of back to back QSOing consisting of some average QSOs and a few rag chews, with a digital thermometer sensor squeezed into the heatsink fins, the heatsink temperature was around 40-45C. Say 20C over ambient. 

In my opinion understanding the equipment you use and its limitations, then treating it always with the respect and kindness it deserves, is key to its long life. 

My 50W amp prototype has been used for around 700 QSOs in the last 9 months. At a guess, that's around 100 hours of operation. In all that time I had one failure of a pair of IRF510s at switch on. Not due to over heat stress. Just a power glitch. I later modified the QCX firnware and added the resistor mod described here http://qrp-labs.com/qcx/qcxmods/ptt.html and flipped the power switch back and forth until I got bored, and couldn't make the glitch destroy anything again. 

So it's quite a robust amp as long as it is used respectfully. 

If you do burn some IRF510s then think of it as fantastic education and the cost of the new ones is the very low price of the education! 

73 Hans G0UPL 


On Sun, Mar 1, 2020, 19:45 George Korper <georgekorper@...> wrote:
THANK YOU HANS,
The paragraph in the 50 PA on heat and is excellent. 
I was waiting for the right  Finals from Digikey, so I tried two different sets
IRF 510's  from Amazon. I can't believe how fast they heat up. What I don't understand
is why. What is wrong inside them? I am saying thank you because, it gave me a small taste of what
your experimenting is like. Buddy, you've got persistence. 

On Sun, Mar 1, 2020 at 11:37 AM George Korper <georgekorper@...> wrote:
THANK YOU ALLISON.  I tried your technique and you know what? 
You saved me from a great deal of grief! Again, I will just say, THANK YOU ALLISON!!!



On Sat, Feb 29, 2020 at 6:27 PM ajparent1/KB1GMX <kb1gmx@...> wrote:
No, none as adding lead length via sockets is a bad thing.

With popper care board damage should  not happen.

Hint if you destroy them,  disassemble, cut the leads at
the package,  (they are dead!) and extract the leads one
at a time with a sufficiently hot iron and tweezer.

Clear the holes by heating the solder and using inertia
(sudden stop while molten) should clear the hole.

Do not drill or use pins or try to poke the tip of the iron in.
That often does more damage.

Allison
-------------------------------
Please reply on list so we can share.
No direct email, it goes to bit bucket due address harvesting in groups.IO


geoff M0ORE
 

Hans,

What are your thoughts on the use of a very thin smear of heatsink compound to assist in the heat transfer. I usually polish both surfaces prior to mounting and use a tiny amount of compound to help get better thermal contact. I confess I haven't read the assembly instructions for the 50 Watt amp but do you suggest a tightening torque for the bolts. The instructions for the 10 Watt Linear amp just says to tighten them but not too tight in case you strip the threads.

It would of course be difficult to supply a tiny amount of compound with the kit, I have a 10ml syringe that I purchased many, many years ago and still have 9ml left!

Geoff

On 01/03/2020 17:14, Hans Summers wrote:
HI George 

Yeah a large number of IRF510s and other MOSFET types perished during my R&D work... some quietly, some very loudly like a gun.

They get hot fast because they are dissipating a LOT of power as heat! So say the thermal resistance from IRF510 to heatsink is 3.5C/Watt and you're dissipating 20W per device, then the temperature rise will be 70C (on top of the current heatsink temperature). Being a relatively small device, their heat capacity is relatively small and so the temperature rise is quite rapid. 

Do NOT sit on the key! Use the amp as for normal CW type of duty cycle and everything will be fine. Normal CW is something around 50% duty cycle on average. 

You want to tune up your antenna? So you want to sit on the key while you make your adjustments? No! You shouldn't be doing that at full power anyway! Tune up at much lower power. 

During all my development I operated sensibly. In an hour of back to back QSOing consisting of some average QSOs and a few rag chews, with a digital thermometer sensor squeezed into the heatsink fins, the heatsink temperature was around 40-45C. Say 20C over ambient. 

In my opinion understanding the equipment you use and its limitations, then treating it always with the respect and kindness it deserves, is key to its long life. 

My 50W amp prototype has been used for around 700 QSOs in the last 9 months. At a guess, that's around 100 hours of operation. In all that time I had one failure of a pair of IRF510s at switch on. Not due to over heat stress. Just a power glitch. I later modified the QCX firnware and added the resistor mod described here http://qrp-labs.com/qcx/qcxmods/ptt.html and flipped the power switch back and forth until I got bored, and couldn't make the glitch destroy anything again. 

So it's quite a robust amp as long as it is used respectfully. 

If you do burn some IRF510s then think of it as fantastic education and the cost of the new ones is the very low price of the education! 

73 Hans G0UPL 


On Sun, Mar 1, 2020, 19:45 George Korper <georgekorper@...> wrote:
THANK YOU HANS,
The paragraph in the 50 PA on heat and is excellent. 
I was waiting for the right  Finals from Digikey, so I tried two different sets
IRF 510's  from Amazon. I can't believe how fast they heat up. What I don't understand
is why. What is wrong inside them? I am saying thank you because, it gave me a small taste of what
your experimenting is like. Buddy, you've got persistence. 

On Sun, Mar 1, 2020 at 11:37 AM George Korper <georgekorper@...> wrote:
THANK YOU ALLISON.  I tried your technique and you know what? 
You saved me from a great deal of grief! Again, I will just say, THANK YOU ALLISON!!!



On Sat, Feb 29, 2020 at 6:27 PM ajparent1/KB1GMX <kb1gmx@...> wrote:
No, none as adding lead length via sockets is a bad thing.

With popper care board damage should  not happen.

Hint if you destroy them,  disassemble, cut the leads at
the package,  (they are dead!) and extract the leads one
at a time with a sufficiently hot iron and tweezer.

Clear the holes by heating the solder and using inertia
(sudden stop while molten) should clear the hole.

Do not drill or use pins or try to poke the tip of the iron in.
That often does more damage.

Allison
-------------------------------
Please reply on list so we can share.
No direct email, it goes to bit bucket due address harvesting in groups.IO


Hans Summers
 

Hi Geoff

I don't believe there is any substantial benefit to the use of heatsink compound in either the 10W Linear or the 50W QCX Amp. 

The thermal resistance of the IRF510 silicon junction to the metal tab is already 3.5C/W. I believe the heat compound just doesn't make enough difference to be important. It isn't harmful, just not necessary. I never use it on any of mine. By all means add some, if is harmless... but I wouldn't bother to buy any heatsink compound if you don't have any. 

In a larger MOSFET device with a much lower internal thermal resistance, then yes it would be very important to improve the tab-to-heatsink thermal resistance by say, a half a C/W because that would be a huge proportion of the total. But in small systems like an IRF510 I don't think it's important.

I have no idea about tightening torque for the bolts, I have no tools for measuring such things nor mechanical engineering expertise to know what are appropriate recommendations. I don't think I'm strong enough to break the thread of the heatsink supplied. What I do sometimes, being right-handed, is tighten bolts using a screwdriver held in my left hand. That way I know what when it comes time to loosen them, I can use my right arm for the task... so I'll always have more power available for un-screwing than was used for the assembly. 

73 Hans G0UPL 


On Sun, Mar 1, 2020, 21:04 geoff M0ORE via Groups.Io <m0ore=tiscali.co.uk@groups.io> wrote:

Hans,

What are your thoughts on the use of a very thin smear of heatsink compound to assist in the heat transfer. I usually polish both surfaces prior to mounting and use a tiny amount of compound to help get better thermal contact. I confess I haven't read the assembly instructions for the 50 Watt amp but do you suggest a tightening torque for the bolts. The instructions for the 10 Watt Linear amp just says to tighten them but not too tight in case you strip the threads.

It would of course be difficult to supply a tiny amount of compound with the kit, I have a 10ml syringe that I purchased many, many years ago and still have 9ml left!

Geoff

On 01/03/2020 17:14, Hans Summers wrote:
HI George 

Yeah a large number of IRF510s and other MOSFET types perished during my R&D work... some quietly, some very loudly like a gun.

They get hot fast because they are dissipating a LOT of power as heat! So say the thermal resistance from IRF510 to heatsink is 3.5C/Watt and you're dissipating 20W per device, then the temperature rise will be 70C (on top of the current heatsink temperature). Being a relatively small device, their heat capacity is relatively small and so the temperature rise is quite rapid. 

Do NOT sit on the key! Use the amp as for normal CW type of duty cycle and everything will be fine. Normal CW is something around 50% duty cycle on average. 

You want to tune up your antenna? So you want to sit on the key while you make your adjustments? No! You shouldn't be doing that at full power anyway! Tune up at much lower power. 

During all my development I operated sensibly. In an hour of back to back QSOing consisting of some average QSOs and a few rag chews, with a digital thermometer sensor squeezed into the heatsink fins, the heatsink temperature was around 40-45C. Say 20C over ambient. 

In my opinion understanding the equipment you use and its limitations, then treating it always with the respect and kindness it deserves, is key to its long life. 

My 50W amp prototype has been used for around 700 QSOs in the last 9 months. At a guess, that's around 100 hours of operation. In all that time I had one failure of a pair of IRF510s at switch on. Not due to over heat stress. Just a power glitch. I later modified the QCX firnware and added the resistor mod described here http://qrp-labs.com/qcx/qcxmods/ptt.html and flipped the power switch back and forth until I got bored, and couldn't make the glitch destroy anything again. 

So it's quite a robust amp as long as it is used respectfully. 

If you do burn some IRF510s then think of it as fantastic education and the cost of the new ones is the very low price of the education! 

73 Hans G0UPL 


On Sun, Mar 1, 2020, 19:45 George Korper <georgekorper@...> wrote:
THANK YOU HANS,
The paragraph in the 50 PA on heat and is excellent. 
I was waiting for the right  Finals from Digikey, so I tried two different sets
IRF 510's  from Amazon. I can't believe how fast they heat up. What I don't understand
is why. What is wrong inside them? I am saying thank you because, it gave me a small taste of what
your experimenting is like. Buddy, you've got persistence. 

On Sun, Mar 1, 2020 at 11:37 AM George Korper <georgekorper@...> wrote:
THANK YOU ALLISON.  I tried your technique and you know what? 
You saved me from a great deal of grief! Again, I will just say, THANK YOU ALLISON!!!



On Sat, Feb 29, 2020 at 6:27 PM ajparent1/KB1GMX <kb1gmx@...> wrote:
No, none as adding lead length via sockets is a bad thing.

With popper care board damage should  not happen.

Hint if you destroy them,  disassemble, cut the leads at
the package,  (they are dead!) and extract the leads one
at a time with a sufficiently hot iron and tweezer.

Clear the holes by heating the solder and using inertia
(sudden stop while molten) should clear the hole.

Do not drill or use pins or try to poke the tip of the iron in.
That often does more damage.

Allison
-------------------------------
Please reply on list so we can share.
No direct email, it goes to bit bucket due address harvesting in groups.IO


ajparent1/KB1GMX
 

Geoff,

Be very careful with heatsink compound (silicone based) as mixed with
soldering the result is very poor.

Also the arctic silver types are conductive so again caution.

For power devices I have a .45kg of Thermaloy 251G for that.
It only needs a very little amount!

Allison
-------------------------------
Please reply on list so we can share.
No direct email, it goes to bit bucket due address harvesting in groups.IO


Glen Leinweber
 

My old National Semiconductor data book shows the IRF510 chip size....
98 thou x 87 thou
2.5mm x 2.2mm
The heat-generating area is a bit smaller than that.
Drain is bonded to the metal tab directly while the source
and the gate are attached with flying leads that conduct very little
heat away.
That chip is a tiny heater bonded to a far bigger slab of metal, which in
turn is molded to the IRF510's black epoxy.

That 3.5 C/W junction-to-tab heat spec is likely due to the small chip
size. The much larger contact area of metal tab -to- heatsink likely
means the tab runs just a bit hotter than the heatsink under it.

We used to rely on the black anodizing on the heat sink as an insulator.
Although the aluminum oxide is very thin, it is a remarkably tough insulator.
This was for 60W Class AB audio, where two transistors bore the heat load.

Not saying you should try this because I don't know the quality of that
heatsink extrusion - a little scratch can cause mayhem. As always,
follow Hans' excellent instructions.


George Korper
 

Hans describes testing six to come up with one, What is the manufacturing difference that makes
the difference and is it consistent? I know it is cheap. Has any manufacturer come up with the same
specs in a better package? Or do similar transistors go for a lot more money? Just want to know to
learn more about these devices, I read the manual and understand Han's logic. Do the Yeasu's and Icom's 
make their own? QST could sure help out by doing a long article on this! 
Also do these Mosfet's do better on 40 than 20?

On Sun, Mar 1, 2020 at 7:04 PM Glen Leinweber <leinwebe@...> wrote:
My old National Semiconductor data book shows the IRF510 chip size....
98 thou x 87 thou
2.5mm x 2.2mm
The heat-generating area is a bit smaller than that.
Drain is bonded to the metal tab directly while the source
and the gate are attached with flying leads that conduct very little
heat away.
That chip is a tiny heater bonded to a far bigger slab of metal, which in
turn is molded to the IRF510's black epoxy.

That 3.5 C/W junction-to-tab heat spec is likely due to the small chip
size. The much larger contact area of metal tab -to- heatsink likely
means the tab runs just a bit hotter than the heatsink under it.

We used to rely on the black anodizing on the heat sink as an insulator.
Although the aluminum oxide is very thin, it is a remarkably tough insulator.
This was for 60W Class AB audio, where two transistors bore the heat load.

Not saying you should try this because I don't know the quality of that
heatsink extrusion - a little scratch can cause mayhem. As always,
follow Hans' excellent instructions.