On Thu, 2009-01-22 at 21:10 +0200, Geoffrey S. Mendelson wrote:
> On Thu, Jan 22, 2009 at 01:45:14PM -0500, Roscoe Primrose wrote:
> >I think the front end in my Argonaut 509 is dead. Noise on 80M last
> >night was S0 on the 509, the same antenna hooked up to my FT817ND was
> >S6-S8... The 509 still passes signal, but the levels are just way
> >down. When I got the 509, the T/R relay was stuck in receive, so the
> >front end being fried wouldn't be surprising.
> >
> >The front end dual gate FET is an MPF132, is there a source for MPF132s,
> >or a substitute available anywhere? I can't find a cross-reference for
> >it anywhere...
>
> A well published upgrade for the 509 (and 505, 515) was to replace the MPF132
> with a 3N211 or the RCA equivalent. It's a drop in replacement, but you really
> should realign the front end when you do it.
>
> The 3N211 has much higher gain, lower noise and built in diodes for
> static/overload protection.
>
> Geoff.
I believe Dan's Small Parts has both 3N211 and MPF131. The 131 will be
very close to the 132 in performance. The 211 is much superior, but
might have a chance of getting regenerative or oscillating if the board
is not well built. The gain of the 211 can be reduced by lowering the
gate 2 voltage.
http://www.danssmallpartsandkits.net/
73, Jerry, K0CQ
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