1-02-12 09.49, skrev Peter Chadwick på Peter_Chadwick@mitel.com följande:
>
> Tom's points are very interesting: I've always been accustomed to switches
> where
> you actually design them yourself on the templates provided by the
> manufacturer,
> so you can decide on make before break, as well as (in some types), fancy
> features such as insulated back contacts, short clips, dummy clips, etc. Non
> US
> readers note that the US terminology doesn't necessarily apply elsewhere, BTW.
> Of course, for home brew, it's a matter of what you can get.
>
> Using a 'progressively shorting' switch may not always be necessary: a
> straight
> forward 'break before make' wired to short out all the unused portion of coil,
> rather than all the taps on the coil, can work just as well. 'Progressively
> shorting' switches are of course limited in the number of positions available.
>
> One problem with rollers is if you need to short just a few turns at the end:
> they can then get very hot. I built one of the 'ultimate transmatch designs';
> that had the problem on 160 of the last two turns overheating. Rewired so as
> not
> to short the unused portion, the strays and the unused L resonated at 14 MHz
> and
> arced over to chassis!
>
> Note Murphy working overtime........
>
> Those switches from Fair Radio are a good bargain, although possibly marginal
> at
> 1500 watts. Cheap enough to keep a spare or two for if they do
> flash......although as the contacts are just hard copper sheet (as opposed to
> annealed), attached with 6-32 brass hardware, they're easily replaceable.
>
> 73
>
> Peter G3RZP
>
>
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>
Why use rollers and switches at all? Series tuning a coil varies the
reactance, doesnt it? Has anybody tried to analyze if this is possible in a
linear? I know WRL once made a ten tube compact linear usng this idea.
Hans SM5KI
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