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Questions tagged [crt]

Anything related to Cathodic Ray Tubes (CRTs), i.e. specially built electronic vacuum tubes where an electron beam is focused and deflected on a phosphor-coated surface in order to display an image.

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What does a grid-cathode bypass capacitor on CRT do, and why is this one not doing it?

I have modified a (US) 1970s solid state B&W TV set for direct (NTSC) composite input for vintage computer use, in accordance with some equally vintage instructions specific to this set. The set ...
BZo's user avatar
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7 votes
4 answers
436 views

CRT vertical deflection problem

I'm getting an odd CRT problem. When cold, the tube has an area about 1/3 way down that isn't scanned. The area above is compressed and the area below a little stretched. I've attached 2 pictures - ...
squelch41's user avatar
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3 votes
1 answer
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Can I use ceramics instead of electrolytic capacitors in CRT drive circuit?

I've been recapping an Amstrad PCW 9256 computer. All the electrotyics are bad on the analogue board - I've replaced the electrolytics I have in stock and the CRT is now working almost perfectly but ...
squelch41's user avatar
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4 votes
2 answers
1k views

Can someone please explain this circuit? SMPS, Bridge Rectifier, Transformer

What do these optional components do? Schematics: https://crtdatabase.com/crts/jvc/jvc-bm-h1300su
Zeus's user avatar
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1 answer
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Vertical wobble and flicker on analog oscilloscope

I'm using an old analog oscilloscope (Metrix ITT instruments OX 725). (I don't have a printed manual for it, but you can find scans of a French user's manual and service manual (with circuit diagrams) ...
Fii's user avatar
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1 answer
773 views

Can a CRT last 100,000 hours or even 300,000?

Online, I could find that high-quality cathode-ray-tube displays (whether be it for a computer monitor or a television set) have a design lifespan of 30,000-50,000 hours of cumulative operation. I ...
CoastCity Lapse 00crashtest's user avatar
8 votes
3 answers
3k views

Why do CRT TVs need a HSYNC pulse in signal?

Could someone, please, explain how old CRT TVs reacted to input signal, specifically to VSYNC and HSYNC pulses? Do these pulses control the electron beam? For instance, if signal would consist only of ...
Scylurus's user avatar
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Silver Coating on the front glass inside a crt

I recently disassembled a defective Macintosh SE. When taking apart the CRT (safely) to preserve the front glass panel to screw back in, i noticed a silver coating on the inside of said front glass ...
Wadafacc's user avatar
2 votes
2 answers
181 views

How did analog color televisions "fix" alignment problems in three-gun systems?

I recall my grandfather panicking when I attempted to adjust the tint on his TV. He said that he would have to call the TV people to come and re-align it. I thought he was crazy at the time, but later ...
Maury Markowitz's user avatar
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1 answer
437 views

Circuit for horizontal and vertical amplifier, homemade oscilloscope

I want to make an oscilloscope with a small black and white TV (crt), currently disconnect the horizontal coil and with this circuit I can see the signals. The problem with this is that only one half ...
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3 votes
5 answers
1k views

Can several CRTs be wired in parallel to one oscilloscope circuit?

I would like to make a 4 channel oscilloscope to view all 4 audio outputs of a quadraphonic amplifier. I can cheaply get 4 of the same type of oscilloscope but would like to have four CRTs side by ...
gazmono's user avatar
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8 votes
1 answer
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Component requires specific voltage and current but the math doesn't add up

I'm trying to get an old soviet era cathode ray tube working. On the data sheet it says the heating element needs between 5.7V and 6.9V, and between 0.54A and 0.66A, but I've measured the resistance ...
Lethe563's user avatar
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1 answer
240 views

Analog oscilloscope trouble

I recently purchased an old HP 130B oscilloscope. While I have experience with old analog oscilloscopes, I have run into an issue with this particular model and before I break anything breaking into ...
Shittykorean4banger's user avatar
4 votes
2 answers
1k views

Why are the vertical deflection coils in a CRT deflection yoke so different from the horizontal coils?

Looking at a typical raster CRT deflection yoke, there appear to be two very different pairs of coils. There is the pair on the inside that curves outwards, and the pair on the outside, which are ...
River E. C.'s user avatar
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1 answer
174 views

How were the phosphors applied to the inside glass tube of older colour CRTs?

I've been reading into how CRTs were assembled and how they work, but I can't seem to find any concise information behind how the coloured phosphors inside the inner glass tube were applied. There is ...
Reggie The Veggie's user avatar
16 votes
4 answers
2k views

Why don't most electrons hit the anode in a cathode ray tube or electron gun?

In a cathode ray tube or electron gun, electrons liberated from the cathode by thermal emission accelerate towards a ring-shaped anode, from the potential difference between cathode and anode. If an ...
sqek's user avatar
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1 answer
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Effects of too-frequent serrations in vertical sync pulse on analog horizontal deflection oscillator

Normal analog TV video signal has a vertical sync pulse with serrations to help keeping the horizontal oscillations in sync. Also, as I understand it, in case of an interlaced video, these serrations ...
Dmitri Urbanowicz's user avatar
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2 answers
113 views

An overview of the inside circuit of a CRT [closed]

I want to know how the inside circuit of a CRT looks, from what I've understood it is that you heat the cathode, then some of the cathode electrons are released, then it gets focused and accelerated ...
Abdo Ismail's user avatar
4 votes
2 answers
1k views

Is it possible to use CRT tubes for audio amplification?

I was wondering if it's possible for me to use the tubes in an old CRT TV to build an audio amp (specifically a guitar amp). If not, would I be able to salvage something else (like an old radio) to ...
Daniel Oren-Ibarra's user avatar
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1 answer
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Thermionic cathode heater filament conundrum

An old CRT I have specifies 6.3 V (DC, I believe) on the heater filament, resulting in a 0.6 A filament current (spec). But I measure the filament resistance as 1.8 Ohm. At V = 6.3 V that would result ...
Gert's user avatar
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Questions about deflection coil interlock on CRT TVs to restore beam brightness control

Electronics noob here, with experience in science and research. I am trying to make a music visulaiser out of an old monochrome CRT TV by connecting the horizontal and vertical deflection coils to an ...
Jonathan Warby's user avatar
0 votes
2 answers
261 views

Fixing composite video distortion caused by brightness changes

I'm modifying an old CRT to take NTSC composite input (it only accepts RF over coax.) I have got a good signal going in but it has this weird distortion going on. When the image is dark the pixels may ...
gonjona's user avatar
1 vote
2 answers
685 views

Mystery Monochrome Monitor

I rescued an old monochrome monitor from the e-waste, but the cord had already been cut. So now I’m trying to see if I can get it working. I know… This is of an era that rather than have a connectors ...
Wes Modes's user avatar
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1 vote
2 answers
198 views

Components of a CRT whine

I noticed something as a kid with my Atari 2600 (and better ears). We can hear the 15khz horizontal freq but I noticed that the whine changes slightly (while the line frequency doesn’t) based on the ...
Thomas's user avatar
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-2 votes
1 answer
159 views

Digital to analog in an old 35mm film recorder [closed]

I'm looking at an old film recorder from 1985, the Polaroid Freeze Frame, the back of the machine pictured here: From here: https://www.radiomuseum.org/r/polaroidco_freezeframe_video_recorder.html I ...
Curiousmarble's user avatar
10 votes
0 answers
523 views
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How to understand a complex diode-resistor function generator circuit?

I'm reverse-engineering a CRT anti-pincushion circuit and it uses a complex diode-resistor circuit to approximate the function \$X-k×X×Y^2\$, where \$X\$ and \$Y\$ are the deflection voltages. My ...
Ken Shirriff's user avatar
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2 votes
0 answers
73 views

Why does changing CRT to HDTV lose antenna channels? [closed]

We have an internal antenna that is connected to a tiny CRT TV through a digital converter box. I recently replaced this CRT TV with an HDTV, and I removed the digital converter box since the HDTV ...
toothandsticks's user avatar
0 votes
2 answers
340 views

Will discharging work if the grounding chassis isn't connected to the mains or otherwise grounded?

Suppose you have a CRT screen and you want to dismantle it for whatever reason. The high-voltage anode needs to be grounded in order to avoid the risk of electrocution. The metal grounding chassis of ...
Some Student's user avatar
1 vote
2 answers
489 views

Neon bulb lamp replacement for surge suppression

I'm restoring an HP 141T and it has a broken neon lamp which is used I believe as surge protection in the following configuration: On the right is the CRT. I believe the only purpose for such lamps ...
cosenmarco's user avatar
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2 answers
337 views

Are fluorescent tubes dangerous?

I'm disassembling a Sega GameGear. The capacitors inside are all rated 50v or lower, so it shouldn't be hazardous in that regard (I will discharge them anyway just to be sure). However, the metal ...
John's user avatar
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1 vote
0 answers
330 views

How to get static on CRT screen instead of black screen?

The TV in question is a Sony Trinitron KV-14M1D CRT. I know it sounds backwards but I need the screen to show white noise for a project (oscillograph); but there seems to be a static block that ...
Zaxarrrr's user avatar
0 votes
3 answers
469 views

Old tvs, how did storing settings work, and what changed in the tv when we tuned a channel?

I don't have an EE background, but I would like to understand some aspects of old TVs. When we tuned channel what exactly changed inside the tv. Was there a circuit card in the tv where something ...
user394334's user avatar
23 votes
7 answers
6k views

How did old television screens with a light grey phosphor create the darker contrast parts of the display?

Many old television screens have a very prominent "light grey" color to the glass, I'm guessing from the phosphor, create darker areas if the effect of electrons make the phosphor glow? Is ...
Zhro's user avatar
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1 vote
1 answer
731 views

How to adjust picture geometry of a CRT TV?

I have a HD CRT TV (Silva Schneider 26 inch) which failed recently. So I took apart a working CRT TV (Philips L01-2E AA, 20 inch) and took its mainboard and connected it properly to the HD CRT tube. ...
MultiMdave's user avatar
0 votes
4 answers
117 views

Geometric information within 1D streams of electrons/photons

How is light—or actually any frequency in the EM spectrum—self-encoding and self-modulating 3D info in its 1D self, so that it “knows,” once it strikes a surface, to discharge all the data perfectly ...
Jordan Fine's user avatar
0 votes
0 answers
210 views

How do I safely discharge this Trinitron CRT when the HV connector seems glued on?

I'm trying to discharge a Sony PVM-1353MD which suffered shipping damage. Unfortunately, I am unable to get my tool under the HV connector. It seems bonded to the CRT with some kind of white silicone ...
user148298's user avatar
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0 votes
1 answer
462 views

Are analog CRT oscilloscope becoming rare? [closed]

Back in the early 2000s I bought cheap Commodore 64 sets from eBay, we were able to get huge collections for under 100 USD. Today they are rare and commensurately expensive! Today you can get analog ...
Gunther Schadow's user avatar
0 votes
4 answers
741 views

Does an isolation transformer make CRTs any safer to work with?

CRT tubes are often described in training materials as huge capacitors capable of delivering very high voltages, often enough to severely injure or cause death. Before working on them, they should be ...
user148298's user avatar
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0 votes
2 answers
160 views

What was the point of an "alignment scope" like Kikusui 5091, and can anything be done about it's dismal horizontal bandwidth?

I got this Kikusui 5091 used for US$ 50 bucks, as a reward for my pretty successful attempt to create a digital raster display from scratch on my oscilloscope, and finishing off my Game of Life in ...
Gunther Schadow's user avatar
-4 votes
1 answer
360 views

Is safe to work with a CRT viewfinder? [closed]

While searching, I found CRTs that run at 5V-12V. These CRTs can run with very low power but is it risky to touch them? You can power these CRTs with 9V batteries but if you lick 9V batteries it ...
IWantJustBasicCollisions's user avatar
0 votes
1 answer
277 views

How would I switch between either of my two outputs into one input?

I am trying to design a circuit which will switch between two RGB outputs into a CRT TV's neck board. Each of the two outputs has three pins. I have tried using the 2N3906 PNP transistor, and it works ...
t0rxe's user avatar
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0 votes
2 answers
192 views

Why do LED/OLED HD and UHD displays have "global refresh rates"?

What is the benefit to scanning vs. individually addressing and updating lines or pixels or screen areas? Is there a standard interface to the majority of HD or UHD displays that allows the ...
Dagelf's user avatar
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0 votes
2 answers
181 views

How do I take proper voltage measurements on device with multiple voltage sources sharing the same ground?

If you recognize me, it's in reference to CRT scopes again. I don't understand how to take proper voltage readings on the circuits. An example is the heating element in the CRT. When I hook both test ...
Jared Cravens's user avatar
11 votes
2 answers
1k views

Image position and size controls vs beam alignment in a color CRT

If you look at a the shadow mask of a color CRT, you can have a pattern like this: Most TVs were purely analog and had knobs to move the picture horizontally and vertically. How does the green gun ...
Thomas's user avatar
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0 votes
0 answers
52 views

Amplifier transistors not receiving change in base voltage... do I look forwards or backwards?

So I'm working on diagnosing a CRT scope that isn't responding to the horizontal controls; the trace is off screen. The two X plates are each being driven by 2 transistors in line. One X plate has ...
Jared Cravens's user avatar
6 votes
5 answers
17k views

What purpose are the transistors serving in this CRT oscilloscope circuit?

So this is part of a CRT oscilloscope diagram, and I don't understand the function of the transistors on the bottom right, Q18 and Q19. Their outputs (41 and 42, crossing through the dotted line) go ...
Jared Cravens's user avatar
3 votes
2 answers
334 views

Does the electron beam go towards the deflection plate with the higher, or the lower voltage?

So I've started tearing apart an old CRT scope to learn everything about them, and right now looking at the voltages on the deflection plates. When the trace goes down, my vertical plates read (a)193v,...
Jared Cravens's user avatar
1 vote
2 answers
787 views

How can chassis ground be used for voltage measurements in a device with components of differing voltages?

The manual for my HV probe tells me to connect my ground clip to the chassis. I can see how this would be good advice for say a 12V car, because the chassis is made the ground and every component uses ...
Jared Cravens's user avatar
9 votes
2 answers
3k views

Fixing old CRT oscilloscopes... what to look for first?

I've been amassing a pretty large collection of these old scopes, and it's about time I got to trying to fix them. About half of the ones I run across and buy don't have traces. I don't need to get ...
Jared Cravens's user avatar
0 votes
1 answer
83 views

Have CRTs ever used a different raking pattern? [closed]

CRTs traditionally scan top-left to bottom-right, in a row-major raking pattern, and appear to have done so since the 1930s. This is a little unusual though, as standard mathematical orientations have ...
Michael Macha's user avatar