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Re: [Amps] teeny copper strap

Subject: Re: [Amps] teeny copper strap
From: Ian White GM3SEK <>
Reply-to: Ian White GM3SEK <>
Date: Wed, 7 Jun 2006 14:10:09 +0100
List-post: <>
Pete Smith wrote:
>Before I mail order some copper flashing or go to one of the lightning 
>protection outfits for far more than I'll need, is there any non-radio 
>source of appropriate stuff for grounding my SB-220 grids?  I think 
>that stained glass makers use copper foil strips, but assume that is 
>probably too thin for what I need.

It's certainly thick enough to carry the RF current. Thanks to the skin 
effect, even very thin copper foil in a 5mm (3/16in) width will carry 
1500W at HF without getting warm (that's 5.5A into 50 ohms).

If it's also wide enough to provide a good low-inductance ground 
connection, it will handle any DC current as well - up to and including 
the large current surge from a you-know-what :-)

As  part of the general upgrade, also consider installing:

*  A 30-ohm 25W glitch resistor in the B+ line (choose a long, thin 
vitreous wirewound resistor to handle any high voltages)

* A step-start circuit, because it allows you to change the mains fuse 
to a fast, low-rated type that will protect the whole amplifier better.

73 from Ian GM3SEK         'In Practice' columnist for RadCom (RSGB)

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