> I thought I should mention that NXP have just announced a new version of
> the BLF578 1200W 50V LDMOS FET called the BLF578XR (Extremely Rugged)
> which is claimed to be "indestructible".
Well, I know a guy who is surely able to destroy even that transistor! ;-)
> Now 50MHz, 70MHz, 144MHz and 432MHz amplifiers should be in the reach of
> us hams with without the fear of destroying an expensive device,
A transistor like this one, packing so much power into a single (and
rather small) package, is extremely hard to cool adequately, at least
when using it in linear service. I think that most hams trying to
casually use such a transistor, without making the correct heat transfer
calculations first, will make it fail from overheating.
But still such ruggedized transistors are welcome, as they should reduce
the need for protective circuits. If anybody melts down a transistor
because of insufficient heatsinking, that's his own fault, and he should
consider it an expensive lesson!
Let's see what the price turns out to be.
> and perhaps LDMOS FETs can now be considered 'like tubes'...
In a way, yes: Being the preferred devices, which tubes were until a few
decades ago (some will say "until today and into the future", but I
don't share that!). On the other hand, the performance and operational
characteristics of LDMOSFETs and tubes are quite different. One can't
very well build a solid state amplifier while thinking tubes.
Meanwhile I keep experimenting. Last thing I built, this morning, was a
formidable power oscillator using two IXTQ460P2 MOSFETs. It was meant to
be an amplifier, but it produced well over 200 watts of output on
roughly 12 MHz even before applying any drive! Nothing that a little
more gate loading won't cure...
Manfred.
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