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
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
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
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
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@...
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
the package, (they are dead!) and extract the leads
at a time with a sufficiently hot iron and tweezer.
Clear the holes by heating the solder and using
(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.
Please reply on list so we can share.
No direct email, it goes to bit bucket due address
harvesting in groups.IO