Oscilloscope homebrew pt 3 (to test electronic components) further developments and more: VLOG
VLOG. Part 3 of “getting a 1970’s CRT” out of the German Democratic Republic (the DDR, out of the 1970’s, with electrostatic deflection) into a working condition. Key information is showed.
Thus: further developments.
First video (21 November 2025) is here
• Electrostatic Cathode Ray Tube B7S2 from E...
Second video 25 november 2025 video is here • Oscilloscope homebrew pt 2 : a first basic...
Thus this, now, 28 November 2025, is a third video about making this oscilloscope circuit (with a static deflection CRT) that can (and will be) perhaps useful.
That is my aim: to test electronic components: coils and capacitors, perhaps also testing semiconductors. Will that succeed? I don’t know, but I have certain idea’s, based on electronics books of the past. In general: that must be possible, when we look to the radio/electronics/physics theory.
Could be that my test circuit will be without a sawtooth generator (= time base) for the horizontal sweep. But it could be that I have to use it…If so: I will publish that on YT.
My first idea is to use the 50 or 60 Hz sine waves out of our mains supply, to be used as horizontal sweep. Inspiration: a book of the 1940’s where they used that idea/setup.
Basic setup (thus): to use this in this simple setup/idea as an indicator, to show certain electrical properties on the CRT screen. I want to use, as first idea, the hor. & vert. plates with 4 x a 500 K resistor to ground (ground=0=null) make them (very) sensitive.
In some circuits (1930’s up to now) some plates (hor. or vert.) are soldered together and/or go both to ground, null. This regards especially the horizontal plates. Depends on the electronic setup, of course.
That is the reason why I use now 4 potentiometers of 500 K, from each plate (2 x hor. and 2 x vert. to ground). I have used 4 protective resistors of 1 K, for all cases where the plates could be driven by a DC or AC source of any kind, to move the “dot” or the “line” to say up-down or right-left.
Of course in such a case the HV driver (transistor, rectifier, coil winding) that does that job must not be overloaded c.q. burn out. By using the 1 K resistors for safety, the minimum DC resistance of the horizontal and vertical plates is always 1 K (=1000 Ohm) to ground, null.
Could be that we have to bridge that resistor with a wire, for certain electronics tests or applications…Say to get a better/more fierce sweep between the hor. or vert. plates, anyway.
That 1 K is quite low, anyway. In my other 3 scopes that I built in the past that resistor (from the hor. or vert. plates to ground) was 50 K.
Please note: the ground/mass of the CRT circuit is on zero, the positive (+) of the HV generator that gives out 1000 Volt (in this case, for the B7S2) to the (+) of the anode is connected to ground (zero). The cathode of the CRT is connected to minus (-) of the HV generator. Electrons are negative (-) they flow to the (+) of the tube screen/anode, connected to ground.
The most negative (-) part in the resistor voltage divider (I have to figure that out, but this is a good idea: 1 M resistors and 1 M potmeters for brightness and focus control, connected between cathode and anode of the CRT, to divide the voltages on the basis of the CRT datasheet: thus giving necessary brightness and focus voltages to the relevant grids) is connected to the brightness grid.
With this tube (the B7S2) that negative voltage (German: “Sperr Spannung”) on G1 (Grid 1) must be between minus (-) 30 and minus (-) 55 Volt. But that can differ somewhat, when you have another CRT with static or electromagnetic deflection.
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Upload 28 november 2025