From Eric

Revision as of 16:27, 10 January 2021

General information about CRT tubes

Some explanations about the functioning of a CRT:

• http://www.cfp-radio.com/realisations/rea75/tv2pouces-01.html
• http://speakyssb.blogspot.com/2016/08/5lo38i-crt-test.html (5LO38I tube)
• This site gives very nice diagrams and explnations about CRTs.
• https://www.circuitstoday.com/crt-cathode-ray-tube
• https://www.aplustopper.com/cathode-ray-oscilloscope-construction-working/

The most popular schematic, from Elextronixandmore, using a Hammond transformer. A kit can be bought at Catahoula Technologies. The schematic and the BOM are here.

Another one solid-state scope from Electronixandmore, without isolation. The voltages are the following:

 HV		350V	Anode Cap
 X1/X2/Y1/Y2	280V	Deflection plates
 A2		270V	Anode 2
 A1		-310V	Anode 1
 K		-665V	Cathode
 G1		-675V	Control Grid

Those values are fine for a 3BP1 tube.

Structure

From https://www.electrical4u.com/cathode-ray-oscilloscope-cro/:

Anode

Cathode

The intensity is controlled by the cathode voltage:

Blanking / grid

The control grid "controls the number of electrons or, indirectly, the intensity of of emitted electrons from cathode". From https://www.circuitstoday.com/crt-cathode-ray-tube: "The grid is kept at negative potential (variable) with respect to cathode and its function is to vary the electron emission and so the brilliancy of the spot on the phosphor screen. The hole in the grid is provided to allow passage for electrons through it and concentrate the beam of electrons along the axis of tube. Electron beam comes out from the control grid through a small hole in it and enters a pre-accelerating anode, which is a hollow cylinder in shape and is at a potential of few hundred volts more positive than the cathode so as to accelerate the electron beam in the electric field." (Note that on several diagrams, the grid is more positive than the cathode... In that case, it accelerates the electrons rather that repeals them. This makes sense if the gate is not used.)

The gate is used for blanking (as its name implies). It is sometimes coupled to the control transistor via a capacitor (because the blanking is only necessary for a short period of time). In order to blank, the gate must be at a smaller

Focus

From https://www.circuitstoday.com/crt-cathode-ray-tube:

Deviations plates

The tubes

5LO38I russian tube

I have bought a russian 5LO38I tube on ebay.

The tube is delivered with a russian notice. Hopefully, someone has provided a german translation translation:

This gives:

• Filament voltage: 6.3V, 600mA +/- 10% (5.7 to 6.9V)
• Anode voltage: 1000V (500V to 1100V)
• Deflection:
  • On X: 0.09 to 0.14 mm/V
  • On Y: 0.11 to 0.16 mm/V
• Focus voltage : 138V to 300V (<550V)
• Cathode voltage: (-125V to 0V)
• G1 voltage: -30V to -90V (-125V to 0V)
• Voltage between "ablenkplatten" and anode: (-660V to 660V)

You can find several applications of the 5LO38I:

• http://danyk.cz/osc_en.html
• http://speakyssb.blogspot.com/2016/08/5lo38i-crt-test.html
• http://www.emartinka.cz/index.asp?IDKategorie=9&IDClanku=18&Akce=clanek
• http://www.labguysworld.com/ES_CRT_DEFLECTION.htm
• http://users.triera.net/zupanbra/osciloskop/Mali_osciloskop.html
• http://www.webx.dk/oz2cpu/clock-scope/scope.htm

Several schematics to generate the high-voltage power supplies:

• From http://danyk.cz/osc_en.html:

• From http://speakyssb.blogspot.com/2016/08/5lo38i-crt-test.html (inspired from http://www.emartinka.cz/index.asp?IDKategorie=9&IDClanku=18&Akce=clanek)

• From http://www.cfp-radio.com/realisations/rea75/tv2pouces-01.html

• From http://www.emartinka.cz/index.asp?IDKategorie=9&IDClanku=18&Akce=clanek

Chinese 8SJ31J tube

See Aliexpress (8SJ31 from GuangYi store (Aliexpress).

The datasheet can be found here : http://www.ges.cz/sheets/8/8sj31jv2.pdf

Deflection circuits

My setup

For the generation of the high voltages, I'll use a 220V/220x2+6.3Vx2 ransformer (bought on AliExpress):

I'll use a Greinacher voltage doubler to generate the -600V. The +220V voltage will be obtained by half-rectifying the transformer's secondary output.

The Greinacher circuit:

Other schematics

• https://www.webx.dk/oz2cpu/clock-scope/scope.htm
• http://www.jogis-roehrenbude.de/Leserbriefe/Scope-Clock/Scope-Clock.htm
• https://web.jfet.org/vclk/

• http://www.catahoulatech.com/index.php?product=KIT-0001|PCB
• http://www.sgitheach.org.uk/scope2.html
• http://ludens.cl/Electron/scope/scope.html
• https://www.eevblog.com/forum/projects/oscilloscope-under-construction/
• https://www.eevblog.com/forum/projects/2-inch-video-monitor/

Other topics

Oscilloscope music:

• https://oscilloscopemusic.com/software.php (a software to generate pictures using X-X modulation))

See also:

• The Dutchtronix oscilloscope clock