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Very interesting! Thanks!
--
John - WA2FZW

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In the discussion on Hackaday they talk about obtaining the counterfeits from

reputable dealers like Digikey and Mouser.? This is interesting because other

similar discussions claim that we should be purchasing from Digikey and

Mouser to avoid counterfeit components from Chinese Ebay vendors.?

Rich got it right.

These devices were originally intended for low frequency switching; they can
handle large currents, but only for a very short time. Their use at RF DEPENDS on
finding a very small gate voltage area which allows linear operation.
Sometimes that area does not exist, even on the originals and true copies.

Some later ones were especially designed for use at RF. They are not MOSFET
switching transistors.

So using a IRF MOSFET is always a case of possible pig in a poke. Some of
them will not work no matter what one does to them. Fortunately, most will work,
but tuning the gate voltage is absolutely critical. At around 5v, there is a sudden release
of ALL available current at the drain to the source. This is the so-called "avalanche" condition.
It must be avoided at all times if using the device for RF (which means that it is harder to
use them when a full-time carrier is involved -- but it van be done).

The other major consideration is the heat generated. These MOSFETS have very poor heat transfer
characteristics. And there is a very small die area where the "switching' work is done. Heat transfer
must be maximized and strictly controlled. Else, poof! There it goes (in milliseconds). It also
very easily breaks into oscillation, especially VHF oscillation. That is controlled by impedance matching of
the drain to the output.

The best tuning is to set the gate voltage low (2v?) without a drain connection. Then connect the
drain supply. Then slowly increase the gate voltage until a SMALL current increase is seen in the drain.
That is getting as close to the linear region as one is able to do with these devices. This is true
(and a characteristic) of all switching MOSFETS. (The major differences are in the peak voltage, the current
each can handle, and the gate capacitances; these vary tremendously according to their die arrangement).
Then connect and adjust your RF source to the drive transistor...this is also just about the recommended procedure
for the BITX40.

These devices work much better at voltages higher than 12v. Those especially designed
for RF use (like the RDHHFxx) devices ARE designed to be used at 12v. Not true for switching MOSFETS.
The RF devices are also much more expensive, but they are more or less guaranteed to work at HF.

There are a few, like the 2N3555, which were in use very early. They are sort of bastard devices with sometimes
good and sometimes bad characteristics. Note that the 2N3555 is really a MOS clone of the 2N3055, a NPN
ordinary transistor. The 2N3055 gained fame as an output transistor in linear power supplies. This was designed
as a MOS replacement, which in fact does run cooler than the original. Doug Demaw was an early investigator of these
devices, and he noted very early on their "odd" characteristics. When the IRF devices first came out, it was
discovered that they could be used as RF devices (much to the design engineers' surprise), but with all the
caveats noted above.

Incidentally, that Hackaday post is a copy of the one he put on his blog. It, and more, are available in full there.

john
AD5YE

I find this post from Allison to be informative, she definitely knows what she's doing: ?
? ? /g/BITX20/message/22597?

There are issues with the IRF510 as an RF amp.
Primary issue is poor thermal conductivity from die to TO-220 tab.
Also, the tab is connected to the drain, not the source as it would be in a good RF device,
so be careful not to short the heatsink to ground! ?(Or add a $0.05 mica insulator and heatsink paste.) ?
The IRF510 does work better at 24v than at 12v, giving better linearity.

But otherwise, Allison reports that the IRF510's ?behavior is similar to
the 10x more expensive RF devices such as the RD16HHF1.
She continues to use the IRF510.

Jerry, KE7ER

--

Yes, but not with the IRF5xx.

Generally speaking, they are DPAK units and require
a secure, solid heat-sink. Also, generally, they are not as well
rated for power out as the TO-220 packages. YRMV.

john
AD5YE

--

Thanks for posting it! Looks like the post has come full circle ;-) I posted this from my blog last week (My blog is the source of the HAD article). Rich has it spot on, though.?
--
Ryan Flowers W7RLF

?

?<-- Learn how to go digital on the BITX40

I considered moving from the IRF510 to the RD16HHF1.
In a TO-220, better heat dissipation, tab is tied to source pin.
Designed specifically for RF service at Bitx40 power levels.
Only 10x the price of an IRF510.

However:
Pins are swapped around a bit from the IRF510, though that's easy enough to accommodate.
Vds max of 50v, vs 100v for the IRF510.
Threshold voltage might be higher than the IRF510, though probably within range for the Bitx40's RV1.

The low Vds max means it's not a good idea to feed an RD16HHF1 PA ?with
more than 12v, whereas the IRF510 does well at 24v.
If I need better than the Bitx40's single IRF510,
will go to a push-pull IRF510 pair like the uBitx or WA2EBY amp.
Beyond that, multiple IRF510's in parallel on each leg of a push-pull amp as Allison is doing.

If swapping in random NFET's for the IRF510, you need to look hard at Vds-max and Vth.
Also the inter-electrode capacitances, this is typically what prevents the use of other switching FET's
meant for use at sub-MHz frequencies, our 2n2219a driver stage simply can't deal with the low impedance load
it sees at RF. ?The IRF510 has an unusually low Qg (the total gate charge).

The IRF510 works fine if it has enough heatsink to keep it cool.
Maybe invest a few pennies in TO-220 insulators and heat paste.
Ideal for experimenters, cheap enough to have a dozen of them on hand in case you have a learning experience.

But as this thread has shown, buy from a reputable distributor, avoid those awesome deals on ebay.
Hard to imagine why anybody bothers to counterfeit the IRF510, as it's under $0.50 in quantity.?

Jerry, KE7ER

Jerry,

The RD16HHF1 is designed for 12.5V, so running at higher voltage is guarantee magic smoke with projectiles!

They have 70 and 100W versions for HF @ 12.5 volts. Maybe worth experimenting!

Raj

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No, I experimented with them for several projects.

They are SO inefficient.? It was so disappointing!? I wasted a lot of time wondering what their appeal was.

Mike, WA6ISP

Hi

Is it possible to attach a Peltier cell to the transistor case to help heat sink?

?

73 de LU5DNM

?

Norberto Modanesi
San Nicolás

----- Original Message -----

From: Ken Hansen

To: [email protected]

Sent: Saturday, July 15, 2017 11:38 AM

Subject: [BITX20] On the subject of fake IRF510

Saw this Hackaday post related to the BITX, thought others might find it interesting.

Ken, N2VIP

-- 
Mike Hagen, WA6ISP
10917 Bryant Street
Yucaipa, Ca. 92399
(909) 918-0058
PayPal ID  "MotDog@..."
Mike@...

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Jerry KE7ER wrote...

But otherwise, Allison reports that the IRF510's
behavior is similar to the 10x more expensive RF
devices such as the RD16HHF1. She continues to
use the IRF510.

I was about to order a handful of IRF510s as it
appears that I am in need of a replacement. Whether
I end up with fakes or real ones, they don't look
too expensive to replace. However, if it became
a habit, it could start to add up. I know there
has been talk of replacements, but are just a
few people losing the finals, or is it becoming
common? I'll definitely be ordering IRF510s to
see how they fare, but if they start to go on
a regular basis, is the RD16HHF1 the logical
replacement? I might experiment with higher voltages
on an IRF510 at some point in time, but my plan
is to operate on 12 to 13.8V most of the time.

--
73 Keith VE7GDH