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Old 26th Jun 2020, 6:30 pm   #21
Top Cap
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Location: Watford, Hertfordshire, UK.
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Default Re: Resistance Decade Box

I made a more conventional model, make before break switches and numbered skirted knobs. It uses 1% 1W, good enough for me at home, the sort of thing you hardly ever use but when you want one ain't you glad you have one.
One thing I strongly suggest is that you provide a Ground terminal and use a conductive enclosure for screening. I painted the inside of my box with conductive paint after suffering from 'hum' when the box was used on the input of an amplifier. The paint was very successful.
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Old 30th Jun 2020, 10:02 am   #22
daviddeakin
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Default Re: Resistance Decade Box

Quote:
in point of fact, the higher-value resistors are the ones that get burnt-out first,
In my line of work I'm more likely to be hooking up the box to a current-limited but high-voltage source, so I'd rather the first 'click' was a 10k resistance than a 1k resistance.

Quote:
am I really the only person to think that using three high-quality, expensive switches with resistors that cost a penny or less is a bit uneconomic?
Not when I got the switches for free! The reason for using high quality switches it for reliability, not to get precise resistance values. I'm clumsy and abuse my tools, but I'm not running a physics laboratory.
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Old 3rd Jul 2020, 9:56 am   #23
daviddeakin
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Default Re: Resistance Decade Box

Casually reading Practical Wireless when I found this fun R-C substitution box design. I'm just putting it here for my own furture reference (March 1958, page 44)
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