I know that because of the DC voltage, you are less subject to hum!
Mike(y)
W3SLK
----- Original Message -----
From: jeff millar <jeff@wa1hco.mv.com>
To: <W8JI@contesting.com>; <amps@contesting.com>; William Fuqua
<Wlfuqu00@pop.uky.edu>
Sent: Wednesday, November 01, 2000 8:48 PM
Subject: Re: [AMPS] DC Filaments???
>
>
> ----- Original Message -----
> From: "Tom Rauch" <w8ji@contesting.com>
> To: "jeff millar" <jeff@wa1hco.mv.com>; <amps@contesting.com>; "William
> Fuqua" <Wlfuqu00@pop.uky.edu>
> Sent: Wednesday, November 01, 2000 12:58 PM
> Subject: Re: [AMPS] DC Filaments???
>
>
> > The only problem is with directly heated filament-cathodes and low
> > bias voltage tubes, the voltage drop across the filament can be a
> > significant portion of the bias voltage. That would mean the filament
> > is not supplying equal current over the entire area of the filament.
>
> Even with AC on the filament, the voltage between grid and filament
> varies along the length of the filament at any instant in time. The
> filament voltage varies very slowly compared to both the RF
> carrier current pulses and most of the modulation envelope.
>
> > That shouldn't hurt life, but it certainly could affect IMD and other
> > parameters.
>
> I can't see how DC could effect IMD. DC creates less variation
> in filament to grid voltage than AC because it doesn't have the
> peaks over RMS that exist with AC.
>
> jeff
>
>
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