General Radio Decade Resistance Box No. 602L
This is a good used GR Decade Resistance Box. Manufactured by General Radio Company in Cambridge, Massachusetts to the highes standards. The case is lined with copper and the ground lug for the copper shielding is on the front panel.
From the catalogue:
"A convenient assembly of resistance cards in a single cabinet with switches is a necessary laboratory accessory wherever electrical measurements are made. Such boxes are constantly used in circuits where a wide range of resistance values is required, as laboratory standards, bridge arms, and dummy generator and load resistors. The TYPE 602 Decade-Resistance Box is an assembly of two or more TYPE 510 Decade-Resistance Units in a single cabinet. Mechanical and electrical protection of the units is provided by the shielded walnut box and aluminum panel, which completely enclose both units and switch contacts. Two-, three-, four-, and five-dial decade assemblies are available. Each decade has eleven contact studs and ten resistance units, so that dials overlap. A detent mechanism assists in setting squarely on the contacts. This permits adjustments to be made without looking at the dials. The resistors are adjusted to have their specified values at their own terminals and not at the terminals of the box. The resistance measured at the box terminals will, therefore, be high by the switch contact and wiring resistance, which amounts to about 0.003 ohm per dial. This method of adjustment has been adopted primarily because no method in which the switch resistance is absorbed in some one unit of a decade can give the correct value of the total resistance for all settings of the various decades. There are also many types of measurement (voltage-divider and substitution bridge measurements, for example) in which the difference in two settings of a resistance box is significant. This difference is given correctly only when the individual resistors have been adjusted independently of switch resistance. The wiring also adds a small inductance, about 0.1 microhenry per decade. The resistance elements have no electrical connection with the shield, which is brought out to a separate terminal on the panel. All General Radio boxes are equally useful on direct and alternating current and maintain their usefulness for many applications well into the radio-frequency range."
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