41 General

4-2. Figure 4-1 is a simplified block diagram of the Model 140A Oscilloscope. Three major circuits are included in the main unit of the oscilloscope: a low-voltage power supply, an amplitude-and-time calibrator, and a high-voltage power supply for the cathode-ray tube. The vertical and horizontal plugins are not part of the main unit, and operate directly into the CRT.

4-3. LOW-VOLTAGE POWER SUPPLY. The low-voltage power supply uses 115/230 volt single-phase power from the line, and generates the following output voltages: +250, +100, -100, and -12.6 volts DC, and 6.3 volts AC. All DC supplies are regulated. Voltages are distributed to the calibrator, the highvoltage power supply, and the vertical and horizontal plug-in units.

4-4. CALIBRATOR. The calibrator uses a 6.3-volt signal from the power transformer to drive a tunnel diode which shapes the signal to a square-wave output. Outputs of 10-volts and 1-volt (peak-to-peak amplitude)

are made available on the front panel as calibrating signals accurate to ±1%. The 1-volt square wave is also applied to the plug-ins for internal use in horizontal and vertical sensitivity calibration.

4-5. fflGH-VOLT AGE POWER SUPPLY. A transistorized oscillator and step-up transformer are used to generate high voltages for the CRT. Both positive (5 kv) and negative (2.5 kv) supplies are used, and are electronically regulated.

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