Decade Voltage Divider Type 654-A N° 130.
Acquistato il 19/11/1938 presso la S.A. Ing. S. Belotti, Milano, come risulta nell`inventario D del 1937 al n° 923 per ₤ 2450, e come si legge su una targhetta sulla cassetta di legno.
Sullo strumento si legge: “Decade Voltage Divider Type 654-A Serial N° 130 General Radio Co. Cambridge Mass. U.S.A.”.
Dal catalogo “General Radio Catalog K 1938” riportiamo le caratteristiche di questo oggetto: « USES: The type 654-A Decade Voltage Divider will supply exact voltage ratios between 0.001 and 1.000 in steps of 0.001, and so is useful on the input of amplifiers and similar high-impedance circuits for reducing the input voltage by a definitely known ratio which can be varied in very small steps. DESCRIPTION: This instrument is equivalent to a pair of TYPE 602 Decade – Resistance Boxes connected in series and so manipulated that as resistance is taken out of one box it is added to the other to maintain the total resistance constant at 10,000 ohms. This action is accomplished through the use of two TYPE 510 Decade-Resistance Units operated from each control knob by means of a chain drive. FEATURES: The TYPE 654-A Decade Voltage Divider covers a very wide range of voltage ratios. It is possible to obtain 1000 different ratios from 0.001 to 1.000, and each one is known with excellent accuracy. The input resistance remains constant regardless of dial settings, and so reaction on the input voltage is eliminated. SPECIFICATIONS
Range: Voltage ratios from 0.001 to 1.000 in steps of 0.001 can be obtained by setting up the desired value on the three switches. Accuracy: Each individual resistor is adjusted within 0.1%, so the error in voltage ratio is never greater than 0.2%. Frequency Characteristics: If the external capacitance which is placed across the output terminals is less than 20 μμf, the frequency error is less than 0.1% for all frequencies below 10,000 cycles. Input Impedance: The input impedance is a constant resistance of 10,000 ohms regardless of the ratio setting. This value is engraved on the panel. Output Impedance: The voltage divider is accurate only when the output impedance is essentially infinite.
Maximum Voltage: The maximum allowable input voltage for a 40° Centigrade temperature rise is 230 volts. This value is engraved on the panel. Temperature Coefficient: The temperature coefficient of the resistors is less than ± 0.002% per degree Centigrade at normal room temperatures. Terminals: Jack -top binding posts are provided and standard ¾-inch spacing is used. The shield is connected to one terminal of both input and output which is marked G. Mounting: The decades are mounted on an aluminum panel which is enclosed in a shielded walnut cabinet. Dimensions: Panel, (length) 13 × (width) 7 inches. Cabinet, (depth) 5¼ inches, over-all. Net Weight: 8¼ pounds».
Foto di Claudio Profumieri, elaborazioni e ricerche di Fabio Panfili.
