[Amps] teeny copper strap

[Pete Smith]

At 09:10 AM 6/7/2006, Ian White GM3SEK wrote:
>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)


The length is a problem with the SB-220's layout - I had a short one in there but a couple of arcs later....


>* 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.


Interesting idea - I thought the CW about the SB-220 was that it had a transformer that was designed to provide a slow start, so that a step-start was really not required.  In any case, the amp has a breaker, so it would be a little more involved.

Thanks for the calcs, Ian - that makes my choices pretty wide open.  And thanks to many for their suggestions, offers to send copper sheet, etc.  I have several leads for local sources now, so won't need to trouble you.

73, Pete N4ZR