How to power-up a CRT ?

[Externet]

Hello all.
To power up a CRT, I believe I need about +10KVDC HV to its anode; some other high +DC voltage called 'focus' derived from that HV resistor divider and another +high voltage called G2? or 'screen' to CRT terminals also from that HV divider.
Heater filament takes 6.3 V for the CRT I have.

Can these 10 KVDC and focus and grid be obtained from a standalone circuit or kit I can buy somewhere ? Like a flyback transformer circuitry that has the focus + screen controls on it ?

Canibalizing a discarded TV can yield most of the circuitry, but do not know how to deal with creating the ~15KHz or other input signals it would need. Guidance, please.

If you have a gadget or device or circuit that makes those voltages, please let me know.
Raster/deflection is not part of what am after. Just want to produce that spot on the screen. no video, no images.

Additional question : A single 30KVDC EHT flyback output that connects to a splitter to supply 3 CRTs ; does it yield three 10 KV for each or each gets 30 KV ?

 

[Externet]

This circuit seen on the web. How does it get the proper oscillation frequency ?

How do you tell if the transformer is for 12V or 160V or whatever ?

 

[danadak]

Jochen's High Voltage Page : Flybacks

Pay attention to his notes about adding MOVs to protect the 2N3055.

Various flybacks -

Regards, Dana.

 

[Nigel Goodwin]

What kind of CRT are you talking about? - assuming it's a colour TV type you need about 25KV for the final anode, and about 8KV for the focus anode - the crude horrible multi-CRT projection sets used 30KV on each CRT. Antique B&W sets used about 12KV to 15KV.

Assuming you're wanting just a 'dot' you should be very, very, aware that you must keep beam current low, as just a dot will cause a permanent burn on the front of the CRT in just a few seconds.

To run a TV type CRT, simply use the board from a CRT TV - you should be able to find plenty going for free, as they just go to landfill.

One extra thought - you should be VERY, VERY careful - as an incorrectly driven (over driven) CRT will pour x-rays out the front of it.

 

[Externet]

Thanks.
Not from a 'normal' TV. It is for one of the 3 CRTs out of a rear projection TV. (green monochrome)
Yes, very aware of burning the phosphor.

Its own printed circuit board is huge to reuse; prefer to make/get something small. Beam travels ~20cm K to A
----> HOW to power ? The one on Dana's link ? And what frequency is that ? And what waveform is that ?

 

[Nigel Goodwin]

Get the schematic for the set, and remove the line output/line oscillator stage components, and power supply components. Build them up in a more compact way. Essentially the line output transistor is just a switch, that 'rings' the tuned transformer, so it's fairly crucial to keep all the tuning parts.

 

[Externet]

The schematic of the original TV seems confusing to me.
I believe the flyback transformer is T8001; its primary is pins 7 to 9. Driven by Q8013 from IC8002 pin 12 as oscillator.
GND is source of Q8013. Do not know why C8037 (at top) is there.

 

[Nigel Goodwin]

Yes, T8001 is the flyback transformer - but it's a very unusual circuit, as it's a half bridge, rather than a single ended line output stage. Because it's a half bridge it requires a coupling capacitor, and that's the function of C8037.

Think of it as an old single supply audio amplifier, with the transformer as the speaker, Q8013 and Q8014 as the push pull output transistors, and C8037 as the speaker coupling capacitor.

 

[Dick Cappels]

Usually the horizontal and vertical frequencies are supplied by a circuit called a sync stripper which is shortly after the broadcast signal is demodulated and detects the sync signals and separates them from the composite video. In some systems, individual H. and V. sync signals are available from the signal source, but that is rare these days. Why run three cables when you can run only one composite signal?

While poking around keep in mind that the anode voltage is very painful! Also never try to measure the focus or anode voltage unless using a high voltage probe rated for that voltage.

As for X-Ray danger, using the part number manufacturer of the CRT this should not be an issue unless the CRT is 60 or 70 years old or more. Tubes generally have pretty good protection built-in, such as the use of high-lead faceplates.

 

[Nigel Goodwin]

Usually the horizontal and vertical frequencies are supplied by a circuit called a sync stripper

I've never heard it called that (unless it's a perculiar American term?) - it's called a 'sync separator' in the TV trade and all the service manuals and books I've ever seen.

 

[danadak]

Google "television synch stripper circuit", plenty of hits, including patent applications.

 

[Nigel Goodwin]

As does "television sync separator circuit"

TI even call their chip "LM1881 Video sync separator".

 

[rjenkinsgb]

TI even call their chip "LM1881 Video sync separator".

I also thought the "sync stripper" was an odd term.
However I did a search for the alternate name - and one of the results is the TI datasheet for the LM1881!

The last bit of section 7.3.1:

Because the original video may also undergo processing, the need for time delay correction will depend on the total system, not just the sync stripper.

Hmmm... I can understand the confusion if even they cannot stick with the same terminology!

 

[danadak]

As does "television sync separator circuit"

TI even call their chip "LM1881 Video sync separator".

National Semiconductor was originator of LM1881.

These folks know the terms - https://antiqueradios.com/forums/viewtopic.php?p=1963599

LM1881 Miniature RGB Sync Stripper / Cleaner PCB DIY Kit

<p>DIY miniature LM1881 Sync Cleaner PCBs with 0805 surface-mount parts. Small format, designed to fit inside SCART plug heads.</p> <p>Used in conjunction with an LM1881 IC to extract CSYNC signals from Composite video inputs for use with RGB-capab

console5.com

 

[Externet]

Thanks. Another name found. It is called separator, stripper, cleaner ... until we find another. And the LM1881 is still of no use: Takes video input to generate the vertical, the horizontal, the sync output, the back porch out...

And I have no video signal to use as input to the chip. The purpose is not displaying video images as in post #1.

Filament input + EHV input + 'screen' input + focus input. ---> Dot on screen output.

 

[Nigel Goodwin]

Thanks. Another name found. It is called separator, stripper, cleaner ... until we find another. And the LM1881 is still of no use: Takes video input to generate the vertical, the horizontal, the sync output, the back porch out...

And I have no video signal to use as input to the chip. The purpose is not displaying video images as in post #1.

Filament input + EHV input + 'screen' input + focus input. ---> Dot on screen output.View attachment 139194

No, of no use whatever to you - apart from if you use an IC line oscillator chip, that 'may' include a sync separator - however, anything 'modern' might use a 'jungle chip', and may well require a processor to set it up via the I2C bus.

Here's a basic 'normal' type of line output stage, using a driver transformer - you just need to feed it with a 15,625Hz square wave - for PAL - but for a spot the frequency doesn't matter.

Television Horizontal Deflection Circuit | Horizontal Output Stage

Television Horizontal Deflection Circuit:The function performed by these circuits is exactly the same as already described for the vertical deflection

www.eeeguide.com

 

[Dick Cappels]

Do we want to spend so much time on obsolete technologies?

In the case of composit video, the the horizontal and vertical sync pulses are combined with the video signals.

In television broadcast receivers this composite video appears at the output of the demodulator.

A sync stripper takes in the composite video and outputs an composite (H + V) sync signal.

A circuit following the sync stripper separates the composite signal into horizontal sync pulses and vertical sync pulses.

TI (Then National) calls the sync stripper function a sync separator, thus the confusion. Hey...they were several miles down the road from most of Silicon Valley video companies, so some differences in naming is reasonable. I could never justify the LM1881 because to me it did the same job as a 20¢ transistor and a few discreet parts.

 

[Nigel Goodwin]

Do we want to spend so much time on obsolete technologies?

In the case of composit video, the the horizontal and vertical sync pulses are combined with the video signals.

In television broadcast receivers this composite video appears at the output of the demodulator.

A sync stripper takes in the composite video and outputs an composite (H + V) sync signal.

A circuit following the sync stripper separates the composite signal into horizontal sync pulses and vertical sync pulses.

TI (Then National) calls the sync stripper function a sync separator, thus the confusion. Hey...they were several miles down the road from most of Silicon Valley video companies, so some differences in naming is reasonable. I could never justify the LM1881 because to me it did the same job as a 20¢ transistor and a few discreet parts.

None of this has anything to do with displaying a spot on a CRT?. But the confusion is from people starting calling a sync separator a sync splitter - presumably one of those Americanism's?, like calling valves tubes.

However, is the OP is just wanting to conform a CRT works? - we commonly used to do just that decades ago, to check if a specific fault was on the chassis or the CRT itself. You simply place two sets back to back, and swap all the CRT connections over, CRT bases, scan coils, EHT leads, not forgetting to connect the aguadag's together. This can be easily done with simple croc clip leads, and if the CRT base lead isn't long enough, then turning one of the sets upside down makes it reach better.

However - BE CAREFUL!!

EHT is too a low a current to harm you - but it's plenty high enough to make you fall and break your neck, or (even more likely) snatch your hand back and shred it across the back of the PCB.