Fig. 1. Schematic for resistor substitution box. 84 73 Magazine * January, 1981

ranged in rows of seven across and four down (See Fig. 1). Then the resistor/switch combinations are connected in series. I used slide switches in my unit (I happened to have them on hand).

The rectangular openings were cut out with a nibbling tool and the switches were mounted to the box pane! with pop rivets.

With the use of 1 % resistors, there is a possible error of ±100k (that's with all resistors in circuit for a total of 9,999,999 Ohms).

With this circuit, there is a possible monetary advantage over conventional resistance substitution boxes which usually require sixty-three resistors and seven ten-position switches to cover the same range.

A Capacitor Substitution Box

A ham shack without a capacitor substitution box?

Fig. 2. Schematic for capacitor substitution box.

I don't believe it. Well, I've been wrong before, so, if yours happens to be without one, build this one.

This capacitor substitution box has a range of from 10 pF to within 10 pF of 1 uF, in 10-pF steps. That amounts to 99,999 possible values. This is done with

■ i.-.-at^i only twenty capacitors and switches. Construction of this unit is simple and straightforward. The capacitors are connected between a common line (B1) and one terminal on each switch The other terminals on the switches are wired to B2. f he switches are arranged in rows of four down

Resistor Substitution Box Parts List


1 Ohm

0 0

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