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[Amps] GU74 and all voltages on the same transformer?

Subject: [Amps] GU74 and all voltages on the same transformer?
From: Ulf Tjerneld <>
Date: Mon, 12 Oct 2009 09:23:26 +0200
List-post: <">>
Hi all,

I'm projecting an amplifier with a GU74B. The transformer I intend to  
use has all voltages; plate, screen and filament on the same core.  
This means that basically all voltages will be applied as soon as the  
step start relay closes. In most literature, such as The Radio  
Handbook, it is very clear that plate and screen never should be  
applied to such a tube before the filament is heated. Now, I have seen  
quite a few builds, both home brewed and commercial, where this is  
actually not put into practice, i.e. plate and screen is applied at  
the same time with the filament. So, now I'm asking for some  
experience with this. Will my tube break if I apply screen and plate  
before the tube is heated? My option here is to get a separate  
filament transformer. It's not a big deal, but I'm curious to know how  
important this is!


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