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Re: [Amps] Filament overwind on an EHT Toroidal

To: Glenn McNeil <>,
Subject: Re: [Amps] Filament overwind on an EHT Toroidal
From: Radio WC6W <>
Date: Thu, 23 Aug 2007 09:22:53 -0700 (PDT)
List-post: <>
Hi Glenn,
  If you reallllly want to go for small & light you
might research using a Microwave Oven Switching
supply, with some additional C on the output, for the
plates.  Someone on this list was investigating that a
while back.  

  A "regular" small switching supply will be fine for
the heaters.  A "soft start" for that application may
be seen here:

73 & Good morning,
  Marv WC6W

--- Glenn McNeil <> wrote:

> G'Day Guys,
> I'm in the early stages of constructing a Twin
> GI-7Bt 144 Mhz Amp...mainly for portable use, hence
> the smaller, cheaper tubes, and I'm looking for only
> 400W Output.
> I am trying to make it as small as possible, and as
> light as posssible. It will be self contained, and I
> have sourced a Toroidal Transformer with two 800v
> windings that I will series up for 1600ac, with 68uf
> of C, hopefully giving me around 2100vDC at 500ma.
> The Toroidal Transformer arrived and has two 6.3v,
> 5amp ac windings, overwound on the outside of the
> thing...if I series these up, I get my 12.6 Filament
> requirement for the two tubes ( 2 amps each at 12.6v
> ). This would save a seperate Filament tranny. 
> Now, on Fault ( I predict one may happen ) , I
> usually use the G3SEK System, and drop off the EHT
> Tranny Primary using a hefty Relay. Using this
> method on my system above would also drop off the
> Filaments, and really complicate things.Hitting
> Reset would see the EHT come back up on Tubes that
> had cooled down due no Filaments. 
> I propose to use a Vacuum Relay in the EHT Supply,
> downstream of the Glitch Resistor, for Fault
> isolation. 
> In case of a fault, the EHT is removed, but
> Filaments left going, as the AC is still on the
> Toroidal Transformer, and in fact, the EHT is still
> up, but isolated from the Tube. 
> I can then decide on what to do next...hit Reset, or
> have a think.
> Am I cutting corners too much in trying to save a
> bit on weight/cost/complexity, and should I drop in
> a toroidal to run just the Filamnets and do things
> in the usual manner ?
> Any comments welcomed !
> 73
> Glenn
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