DIY Minimalist Oscilloscope: Build Your 300V Tube Scope

Circuit diagram:

Description

Individuals who possess vintage cathode ray tube oscilloscopes may find renewed interest in utilizing them for their original intended application. Successful operation requires careful application of specific voltages to designated pins. Often, detailed part numbers are absent, necessitating meticulous examination of the tube’s internal construction to identify the correct connections for acceleration and deflection electrodes. The device utilized for these tests was a 7 cm model with an undetermined origin.

Initially, it is crucial to determine the function of each pin – specifically, those associated with the heater, cathode, grids, deflection plates, and anode. Following this identification, a basic oscilloscope can be assembled by connecting the Y input through a suitable capacitor to one of the Y deflection plates. For the X deflection, a neon lamp oscillator is employed to generate a timebase, while a focus regulator circuit completes the system.

The operation of the horizontal deflection oscillator is clearly observable as the subtle pulsing of the neon lamp. Whenever the voltage across the parallel-connected capacitor exceeds the lamp’s strike voltage, a brief current pulse discharges it, effectively resetting the capacitor. This method offers a remarkably straightforward approach to generating a sawtooth waveform. A supply voltage of 300 V is sufficient for uncomplicated experiments, even though the tube is rated for operation at 1000 V or higher.

More about components

Integrated circuits (ICs) frequently play a vital role in electronic circuits, offering compact and efficient solutions for signal processing and amplification. One common example is the LM358, a dual operational amplifier. This IC consists of two independent amplifier stages, providing high gain and excellent performance. It is widely used in low-voltage, low-current applications such as instrumentation amplifiers, signal conditioning circuits, and general-purpose amplifier circuits. The LM358 is typically housed in a 8-pin DIP package and operates over a temperature range of -40°C to +85°C. Another frequently used IC is the 555 Timer, a versatile chip capable of generating various waveforms, including pulse widths, tones, and clocks. This IC contains a monolithic integrated circuit that is used to generate time delays. It's a popular choice for building timer circuits, oscillators, and pulse generators.

Furthermore, the 74HC14 is a commonly used hex inverter IC. This IC provides six independent outputs that are the inverted versions of the inputs. The 74HC14 is generally packaged in an 8-pin DIP package, and it is widely applied in logic circuits, data processing, and control systems. It offers high input impedance, good noise immunity, and fast switching speeds, making it suitable for digital applications.

It must be admitted that this design’s sensitivity, linearity, trace size, bandwidth, and triggering facilities leave something to be desired. However, it has been demonstrated how minimal circuitry is required to produce a fully functional oscilloscope.