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[Amps] filament choke questions

Subject: [Amps] filament choke questions
From: Paul Decker <>
Date: Wed, 7 Oct 2009 15:45:03 +0000 (UTC)
List-post: <">>

Hi Guys, 

I'm making more and more progress on my amp, thanks for all of the help 
answering questions and such, it's appreciated.   Some have asked for pictures, 
I'll post some shortly. 

Here is another one.  I'm using a schematic from the 1995 ARRL handbook, a 
50Mhz 3cx800A7 amplifier.   I'm wiring up the filaments now looking at the 
choke between the feed through caps and the actual heater, it says: 

"RFC2 - 14 turns #16 enameled wire on a 1/2 inch-OD ferrite rod.  See text." 

The text then says:  "RFC2 is bifilar wound on a ferrite rod" 

First question - What is the purpose of this choke?  I assume to keep input RF 
out of the filament power supply. 

Second - What kind of ferrite rod, any material?  How important is it, I have a 
rod from an old 4:1 balun , will any approximate 1/2 inch  rod work?   


Paul (KG7HF) 

----- Original Message ----- 
From: "Paul Decker" <> 
Sent: Monday, October 5, 2009 3:35:23 PM GMT -05:00 US/Canada Eastern 
Subject: filament voltage 

Hi Guys, 

I want to quickly double check my understanding of filament voltage. 

When the datasheet specifies 13.5 +- 0.6 V, such as with the 3cx800A7, are they 
referring to a DC voltage?   So, if I have 13.5 VAC, the RMS value, it would be 
just dandy, or are they referring that 13.5 V is the maximum peak value? 

Paul (KG7HF) 
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