VFO-62

At your national Distributors now! The first self-powered variable frequency oscillator for 6 and 2 meter operation! Self-powered, self-contained. Plugs into 117v AC outlet and transmitter crystal socket. Provides front panel crystal control without changing connections; has phone jack, precision vernier dial, and provision for remote standby/operate control. Low power drain (18 watts) allows 24-hour operation for pennies a day.

The National VFO-62, is a precision variable frequency oscilla- tor for the 2- and 6-meter bands. The VFO-62 is designed to operate with most equipment using crystal oscillators operating in the 8- to 9-mc region or with most equipment using overtone oscillators in the 25- to 27-mc range.

Easy installation is provided, since the low- level RF-output signal developed by the VFO-62 can be connected directly to the crystal socket of existing commercial transmitters. Provisions for crystal operation are provided in the VFO-62 without the necessity of changing interconnect- ing cables.

Circuit Description: Your VFO-62 is a com- pletely self-contained unit which operates from a 105-125 volts ac power source. The unit uses a full-wave rectifier and two vacuum tubes, includ- ing a voltage regulator and a dual-purpose oscilla- tor-output stage to develop the RF signal.

The oscillator section employs the triode half of a 6BH8 tube as a tuned-grid tuned-plate oscil- lator, with the plate-tank circuit fixed tuned at approximately 9.5 mc. This eliminates the neces- sity of tracking and peaking the plate circuit while obtaining reliable oscillation over the entire op- erating band (8 to 9 mc). The oscillator covers the 6-meter band by using the 6th harmonic of its fundamental output frequency range (8.33 to 9.00 mc) and the 2-meter band by using the 18th harmonic of its 8.00- to 8.33-mc range. When the BAND switch is in the X position the variable tuned circuits are disconnected, and the funda- mental oscillator becomes crystal-controlled, pro- vided a crystal is inserted in the front panel socket. To attenuate the effects of output loading, a very low value coupling capacitor (10 mmfd) is used to provide a high degree of isolation between the oscillator and output stages. During normal operation (FUNCTION switch in OPR or STBY), the output stage is a cathode follower with an output impedance of approximately 100 ohms. If a 1-mc crystal is inserted in the calibration crystal socket and the FUNCTION switch is in the CAL position, the cathode follower is con- verted to a crystal-controlled Pierce oscilla- tor, which is used for internal calibration. When the FUNCTION switch is placed in the CAL posi- tion, both the fundamental and calibrating oscil- lators are operating, and heat notes are developed in the audio load in the plate circuit of the output stage. This output is coupled to the headset jack (J1) at the rear of the unit. Standby provisions are incorporated in the cathode of the fundamental oscillator circuit. The cathode is connected to the FUNCTION switch and rear terminals so that the oscillator may be made operative by the front panel control of the VFO-62 or by a remote shorting contact. DC voltages for the unit are provided by a full-wave power supply. The output of the power supply is held constant by an OB2 voltage regulator.

PHYSICAL SPECIFICATIONS: 6 1/2" wide x 5 1/4" high x 5 1/2" deep, 6 lbs

Source: The National VFO-62 Instruction Manual and 1958 QSTs.

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