Oscilloscope

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* https://www.circuitstoday.com/crt-cathode-ray-tube
* https://www.circuitstoday.com/crt-cathode-ray-tube
* https://www.aplustopper.com/cathode-ray-oscilloscope-construction-working/
* https://www.aplustopper.com/cathode-ray-oscilloscope-construction-working/
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The [http://www.electronixandmore.com/projects/simplescope/index.html most popular schematic], from Elextronixandmore, using a Hammond transformer. A kit can be bought at [http://www.catahoulatech.com/index.php?product=KIT-0001 Catahoula Technologies]. The schematic and the BOM are [http://www.catahoulatech.com/products/KIT-0001/OscilloscopeCrtDriverData.pdf here].  
The [http://www.electronixandmore.com/projects/simplescope/index.html most popular schematic], from Elextronixandmore, using a Hammond transformer. A kit can be bought at [http://www.catahoulatech.com/index.php?product=KIT-0001 Catahoula Technologies]. The schematic and the BOM are [http://www.catahoulatech.com/products/KIT-0001/OscilloscopeCrtDriverData.pdf here].  
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== Anode ==
== Anode ==
-
== Cathode ==
+
== Cathode control ==
The intensity is controlled by the cathode voltage:
The intensity is controlled by the cathode voltage:
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[[File:crt-intensity-control-2.jpg|400px|thumb|none]]
[[File:crt-intensity-control-2.jpg|400px|thumb|none]]
-
== Blanking / grid ==
+
On some schematics, the intensity is controled by the gate (that's a bit strange...):
 +
 
 +
[[File:5LO38I-hv-4.jpg|400px|thumb|none]]
 +
 
 +
== Blanking / grid control ==
The control grid "controls the number of electrons or, indirectly, the intensity of of emitted electrons from cathode".
The control grid "controls the number of electrons or, indirectly, the intensity of of emitted electrons from cathode".
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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."  
+
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."
-
(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
 
 +
From https://www.sciencedirect.com/topics/engineering/cathode-ray-tube: "These electrons have to pass through a pinhole in a metal plate, the control grid. The movement of the electrons through this hole can be controlled by altering the voltage of the grid, and a typical voltage would be some 50 V negative compared to the cathode. At some value of negative grid voltage, the repelling effect of a negative voltage on electrons will be greater than the attraction of the large positive voltage at the far end of the tube, and no electrons will pass the grid: this is the condition we call cut-off."
-
== Focus ==
+
(Note that on several diagrams, the grid is more positive than the cathode... In that case, it accelerates the electrons rather that repells 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
 +
[[File:crt-gate-2.jpg|400px|thumb|none]]
 +
 
 +
== Focus control ==
From https://www.circuitstoday.com/crt-cathode-ray-tube:
From https://www.circuitstoday.com/crt-cathode-ray-tube:
[[File:crt-focus-1.jpg|400px|thumb|none]]
[[File:crt-focus-1.jpg|400px|thumb|none]]
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== Deviations plates ==
+
== Deviations plates control ==
 +
 
 +
[[File:deflection_1.jpg|400px|thumb|none]]
 +
[[File:deflection_2.jpg|400px|thumb|none]]
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The datasheet can be found here : http://www.ges.cz/sheets/8/8sj31jv2.pdf
The datasheet can be found here : http://www.ges.cz/sheets/8/8sj31jv2.pdf
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= Deflection circuits =
 
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[[File:deflection_1.jpg|400px|thumb|none]]
 
-
[[File:deflection_2.jpg|400px|thumb|none]]
 

Revision as of 16:49, 10 January 2021

Contents

General information about CRT tubes

Some explanations about the functioning of a CRT:

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.

Elextronixandmore.jpg

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/:

Crt-structure-1.jpg

Anode

Cathode control

The intensity is controlled by the cathode voltage:

Crt-intensity-control-1.jpg
Crt-intensity-control-2.jpg

On some schematics, the intensity is controled by the gate (that's a bit strange...):

5LO38I-hv-4.jpg

Blanking / grid control

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."


From https://www.sciencedirect.com/topics/engineering/cathode-ray-tube: "These electrons have to pass through a pinhole in a metal plate, the control grid. The movement of the electrons through this hole can be controlled by altering the voltage of the grid, and a typical voltage would be some 50 V negative compared to the cathode. At some value of negative grid voltage, the repelling effect of a negative voltage on electrons will be greater than the attraction of the large positive voltage at the far end of the tube, and no electrons will pass the grid: this is the condition we call cut-off."


(Note that on several diagrams, the grid is more positive than the cathode... In that case, it accelerates the electrons rather that repells 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

Crt-gate-2.jpg

Focus control

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

Crt-focus-1.jpg

Deviations plates control

Deflection 1.jpg
Deflection 2.jpg


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:

5LO38I-datasheet.jpg

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:

Several schematics to generate the high-voltage power supplies:

5LO38I-hv-1.jpg
5LO38I-hv-2.jpg
5LO38I-hv-3.jpg
5LO38I-hv-4.jpg
5LO38I-hv-5.jpg

Chinese 8SJ31J tube

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

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


My setup

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

Transformer for tube.jpg

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:

Greinacher.jpg

Other schematics


Other topics

Oscilloscope music:

See also:

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