[Amps] Switching Supplies for High Current Filaments

[David Cutter]

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 at yahoo.com>
To: "Paul Decker" <kg7hf at comcast.net>; <amps at 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/