VN88 Fets as linear amp
 

On Tue, 03 Aug 2004 19:36:19 +1000, Alan Peake
wrote:

Hi all,
Has anyone had experience with the Siliconix Vmos VN88? I've got a
pair running as a 1W linear on 40M and 80M but I've no idea of their
potential. They seem to have a much higher input impedance than
equivalently powered bipolars but I really don't have much of a feel for
this.
Any ideas on maximising ouput would be greatly appreciated,
Alan

They are obsolete now, I'm afraid. Not exactly a great choice for this
application. You'd be better off picking a newer, more suitable Mosfet
and starting from scratch if it's more power you're interested in.
BTW, it's a characteristic of all Mosfets to have a *very* high input
impedance as virtually no current flows through the gate, they're very
easy to drive, especially for types with a low gate/source capacitance
figure.
--

"What is now proved was once only imagin'd." - William Blake, 1793.

In article , says...
Alan Peake wrote:
Thanks for that. I'm only using VN88s because I had some - there are no
nearby RF FET shops here :)

Maybe they'll open an RF FETs 'R' Us soon?

Seriously, it seems to be getting worse, at least around here. The Active
Electronics store that opened a few years ago is now closed, and one of
the big distributors in the area abruptly disappeared (not the building,
but apparently all of its contents and employees). That leaves a new
Fry's, which doesn't seem to be much for semiconductors, and one old
dependable TV parts distributor 50 miles from here... and, of course,
a few places with $50 minimum orders who don't seem to like cash or
checks.


Don't forget Alphatronics in Southcenter (or Supertronics, or whatever
they're calling themselves these days). Whenever I go to Fry's, I
usually end up need to go by there for something Fry's didn't have, and
vice versa.

Fry's actually does pretty well in the semiconductor department if you
don't mind using NTE crossrefs for everything. They are better at
stocking semiconductors than, say, resistors.

-- jm

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