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RPTV CRT tube conversion to oscilloscope

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RODALCO

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Hi Electrotech friends ,

To be honest I have two oscilloscopes at home anyway, but this is more of a challenge I am currently pondering about.

I have watched various YouTube video's of CRT TV's converted into simple oscilloscopes, or just music display devices, more like a bit of fun, and not for accuracy at all, and some results look pretty bad anyway.

At the moment I am fiddling around with some 14" TV's (Magnetic Fields video) and learning as I go, as I have not too much knowledge how TV's work, but working daily with 11000, 22000 and 33000 Volts at a few hundred Amps in the Power board, and am careful with High Voltage protocol.

To run a normal CRT TV the horizontal coil needs to be in circuit as otherwise the TV shuts down. ( This has the high frequency scanning rate)
I have disconnected the vertical coil and via variac and transformer I can control the Vertical projection.

My idea is to drive a monochromatic RPTV Tube from the 14" TV flyback driver board, the Ultor Cap and HV focus etc. and control the deflection coils from an auxillary source.
The existing 14" TV deflection coils can be used as dummy ballast to keep the TV board working.
The way I look at it as long the coil impedance values are more or less the same it should work in principal.

I wonder if a monochromatic tube from a RPTV could be used.
I have three complete RPTV's at home all with the CRT's in it.
To make a monochromatic Red, or Blue or Green display would be cool.

Photo's and findings will be posted in due course.

Just not 100 % sure how to connect the tube up. Will attach a photo shortly.
 

RODALCO

Well-Known Member
WIN_20160610_171517.JPG WIN_20160610_171539.JPG
 

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RODALCO

Well-Known Member
The CRT's are 9 plus 1 pin devices
These were loose ones I had laying about, one is broken.
H terminals are heater 6.3 Volts
G1 gate 1?
G2 gate 2?
K not sure
This one has to be the blue CRT as per markings.
 

spec

Well-Known Member
Most Helpful Member
Normally:

G1= Grid 1
G2= Grid 2
K= Cathode

I suggest it would be best to keep both the original line and frame coils with the CRT. Also, the focusing and correction magnets etc and the associated electronics, anode voltages EHT, etc, as these are tailored to the CRT characteristics.

You could probably disconnect the line coil from the line drive circuits (line output transformer) by putting a dummy line coil from another set or even making a suitable inductor to load the line drive circuit.

About the coil driver electronics: the transfer function, horizontal and vertical coil current versus deflection distance, are non linear, especially with wide angle, flat-faced CRTs. This nonlinear transfer function is corrected by shaping circuits in the horizontal and vertical coil driver circuits.

To drive the line and frame coils a voltage to current amplifier would be required. This would look like a modified audio power amplifier.

I know you have not asked this question, but the best way to convert a TV into an oscilloscope is to use the TV as a monitor and make a digital storage scope circuit that would feed the RF input or video input of a normal TV.

The beauty of this approach is that the performance would be better and the scope circuit could potentially be used with any TV or monitor.

spec
 
Last edited:

Nigel Goodwin

Super Moderator
Most Helpful Member
I know you have not asked this question, but the best way to convert a TV into an oscilloscope is to use the TV as a monitor and make a digital storage scope circuit that would feed the RF input or video input of a normal TV.
Exactly, driving the CRT directly (using scan coils) gives a VERY poor performing and VERY lo-spec scope.
 
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