Photo 1 Frontview of the oscilloscope 

The circuit is absolutely convential and does not use any fancy stuff.

A reliable timebasecircuit (read sawtooth generator) up till 100 KHz is realized with no-nonsense components (3 times a BC547 transistor and some regular resistors and capacitors). The flyback suppression signal is also derived from this small circuit. I have not included the circuit of the generator since one can find similar circuits anywhere on the www.The sawtooth signal is brought to the proper level by the X-deflection amplifier.

The X- and Y-deflection amplifiers are very identical. Two transistors BF259 per amplifier are the centre of this circuitry. The circuits were built-up on VERO-board.

 Principle of the X - deflection amplifier. Except for the SYNC-output, the Y-amp is identical

The Y-amplifier receives its steering input signal from the preamplifier. This preamplifier uses some simple LF opamps (741). With a multiple position switch the amplification is controllable over a wide range.

Most important component in the scope is the (Philips) 3BP1A tube, the CRT (Cathode Ray Tube). This small tube with its 7.5 cm wide screen produces a nice, green glow, or sharp lines if you like. I do not know whether this tube is widely available these days, but I had one in my junkbox and because of the beauty of this magic eye, it had to be used.

A piece of transparant persplex had been mounted onto the front of the old PC housing. You can see the 3BP1A right behind it. De persplex plate has two goals: to protect the tube from agressive intruders and to carry a scale indication.

The presence of mu-metal around the 3BP1A was an absolute must. Without this shielding, the influence of external elektrostatic (and also -dynamic) fields was such, that any control of the electron beam became impossible. I got the mu-metal from an unserviceable transformer (from an audio preamplifier).

A Canadian website provides following characteristics for the 3BP1A:

575 VDC can be produced by a simple cascade circuit (use though diodes and capacitors; old TV components proved to be very reliable) .

Some potentiometers take care for the adjustment of astigmatism, X-shift, Y-shift, focus, brightness, and sync. Multiposition switches were used for the timebase selection (max. 100 KHz) and vertical sensitivity (max. till 0.01 V/cm).

The 3BP1A (diameter 7.5 cm, length approximately 25 cm)

The results

For measurements of signals with a repetition frequency of up till about 100 KHz, this versatile oscilloscope is your choice. Above this cut-off frequency you can forget it; the sensitivity rapidly decreases.

The resolution of the picture track is fine. Very sharp pictures can be obtained if focus, brightness and astigmatism are adjusted in the proper way.