Yes, an FET built for RF will be somewhat better behaved.
More linear, a wider Vgs active region, less gate capacitance, a tab at ground potential.
But I think Farhan made the right call to use the IRF510 for a $109 ($59 if the Bitx40) radio.
It's popular on amateur transmitters for a reason.? It's very cheap and it can work quite well.
Reread KB1GMX's post:? ?
/g/BITX20/message/22597and check the web for complaints about the WA2EBY amp:
? ??
? ??
I doubt most failure modes we see reported here happen in microseconds.
Just be careful with the gate bias control, and use a large enough heatsink to keep the IRF510's cool.
With a proper design, KB1GMX reports most failures are due to too small a heatsink.
If you disagree, go ahead and invest in what you consider a proper FET.
But keep in mind that 99% of the folks reading this forum will stick with the IRF510's.
Yes, the power amp final needs improvement, just like the? ptt pops and lack of agc
and too skinny volume control shaft and flaky CW keying.
A working radio when built as documented on hfsignals.com, but screaming to be tinkered with.
Exactly what I wanted.
Yes, the IRF510 was designed for switching service at much lower frequencies.
So what?? The WA2EBY amp using IRF510's in push-pull works fine across all of HF.
Jerry, KE7ER
On Mon, Jan 29, 2018 at 02:33 pm, John Backo wrote:
I think Sarma is right. The IRFxxx MOSFETS are
really on/off switches. They have a small linear region which
can be used for RF, but they are really designed to be "all on" or "all off".
That means that once they start conducting, they are very fast.
Whatever happens takes microseconds to accomplish. What
device is fast enough to stop that? That is the real question.
And even several amperes over a micro-sized circuit for even a few
microseconds represents a lot of joules of energy...which is why it
is relatively easy to blow up a IRF510. It goes along with the design...
