[Fwd: Re: [TenTec] Amps for QRP rigs]

[Dr. Gerald N. Johnson, P.E.]

Message-ID: <354A8F83.5927@ames.net>
Date: Fri, 01 May 1998 22:15:06 -0500
From: "Dr. Gerald N. Johnson, P.E." <geraldj@ames.net>
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Organization: Gerald N. Johnson, P.E.
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To: Al Gulseth <agulseth@juno.com>
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Subject: Re: [TenTec] Amps for QRP rigs
References: <19980501.211637.5039.1.agulseth@juno.com>
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The IRF510 is almost uniquely suited for rf having an input C of about
120 pf. Nearly all the rest (except maybe the IRF 710 and 711, and 511)
have an input C of about 1000 pf or more which is what WE think of as a
bypass capacitor, not something to tune a resonant circuit with. The 710
and 711 would probably not work any better than the 510 at 12 volts but
might be really interesting (though needing neutralization) at 120 or
200 volts on the drain(s). The input C (and gate to drain C) does change
with applied gate and drain voltage so keeping the power mosfet calm can
be a problem. I think maybe both problems can be licked in grounded gate
circuit, but havn't yet tried it.

73, Jerry, K0CQ


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