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[Amps] Filament overwind on an EHT Toroidal

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Subject: [Amps] Filament overwind on an EHT Toroidal
From: "Glenn McNeil" <>
Date: Wed, 22 Aug 2007 22:39:10 -0000
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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 

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 !

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