It's all a matter of filtering. Hitherto, valve heaters receive a low noise
source of electrickery, but with this idea, there could be considerable
noise from the switching waveform. Computer and other dc supplies with
which I am familiar have 100mV of noise (it doesn't need to be any better)
in quite a wide spectrum (don't ask me to define it - look on a spectrum
analyser). Multiply this by the system gain in GG directly heated mode and
see if that equates to a big signal on the output of your amplifier. If it
does, add more filtering to the switcher. The heater choke will help in
this. I am talking about dc not using the switching waveform itself.
W6CW's slow start looks good.
David
G3UNA
----- Original Message -----
From: "Radio WC6W" <wc6w_amps@yahoo.com>
To: "Paul Decker" <kg7hf@comcast.net>; <amps@contesting.com>
Sent: Thursday, October 07, 2010 6:33 PM
Subject: Re: [Amps] Switching Supplies for High Current Filaments
> Hi Paul,
> Acceptable on an indirectly heated tube.
>
> This will cause trouble on a filamentary type as even though the filament
> is structured to minimize the effect some modulation will occur. This is
> not generally noticable with (50-)60Hz operation but, at 20-100Khz the
> sidebands will be evident.
>
> Also on a GG design, the filament choke will have substantial reactance
> at the switcher frequency creating more problems...
>
> 73 & Good morning,
> Marv WC6W
>
> http://qsl.net/wc6w/
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