Figure 2. Schematic diagram of the voltage regulator

unit fits the battery compartment of the oscillator and need not be permanently installed. The shift from batteries to a-c supply and vice versa can be made in a few seconds, so that the oscillator can be used with a-c supply in the laboratory and with batteries in the field.

Figure 1 is a photograph of the power supply unit itself and Figure 2 shows it installed in the oscillator cabinet. On recent models of the oscillator (Serial No. 402 and above), the ON-OFF switch is arranged to break the a-c line feeding the power supply. On older models.

where the panel switch breaks only the filament circuit, the plate supply can be turned off by using a switch provided on the Type 613-PI Unit, or a new switch can be installed in the oscillator by the user.

The circuit of the power supply unit is shown in Figure 3. In the low-voltage circuit for supplying the filaments, a copper-oxide rectifier with adequate filtering is used. The usual thermionic rectifier is used in the high-voltage circuit.

One important feature is the built-in voltage regulator which keeps the output voltage constant over a wide range of line voltages. This is a vacuum-tube type of regulator and is shown in simple form in Figure 4. When the ratio —r is made

Ri equal to the amplification constant of the vacuum tube, constant voltage is obtained at the output terminals for a wide range of input voltages. By means of the bias Eg the output voltage can be adjusted to the desired value. In the Type 613-P1 Power Supply, the bias Eg is obtained from the constant voltage drop

Figure 3. Interior view of the Type 613-P1 Power Supply

Figure 3. Interior view of the Type 613-P1 Power Supply

across the neon lamp, 1-3, and is adjustable by means of the slider 011 R-7.

Excellent voltage regulation is provided by using this system. With the normal load of the Type 613-B Beat-P'requency Oscillator, the output voltage varies between 134 and 137 volts for a line voltage range of 100 to 130 volts.

The line-frequency hum level has been kept low by using adequate filtering and by providing an electrostatic shield between the primary and secondary windings of the power transformer. The hum amplitude appearing in the oscillator output is less than 2 millivolts for all line voltage and frequency combinations except 120-130 volts, 42 cycles, where it rises to 3 millivolts. This is equivalent to about 0.01% of open circuit output voltage.

This instrument will operate on all line frequencies between 40 and 60 cycles. Total power input is approximately 15 watts.

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