There is no set number. It varies, to match the inductance required by the flyback transformer and vertical output stage.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
At this point in time I'm not interested so much in HF stuff(except looking at noise, say)... I mainly just want something to view the output of simple circuits so I can have a visual idea if they are working or not.... such as from a simple regulated power supply I need to make(instead of guessing that its working when I measure the output voltage and it happens to be what I want).
yeah, I guess thats what I will do...
Thanks, Jon
What does that matter? do you mean that since they drive the coils with there transformer they have to worry about the inductance of the coil?
I don't plan on using the TV's power supply(atleast at this point) to drive the coils so I don't see how I have to worry about that...
Jon
It means that I just want to visualize whats going on instead of guessing. I don't care if I'm off a 1V out of 10 or if the plot is distorted due to the nonlinear deflection of the tube or whatever... Just seeing a simple plot is good enough for me.. for now atleast. I'll probably try to get me a real oscilloscope soon but until then I'd like to play around with the TV one for fun and to see what I can learn from it.
?? ;)
Thanks Jon
Sure there is... its a good learning experience.
I had a computer monitor but now its gone ;/ really sucks... but the TV will do for now until I can find a real oscilloscope.
Thanks, Jon
In the electrostatic deflection do they just use plates as most examples on oscilloscopes shows? Could I replace the coils with plates or would they be to far apart?
Thanks, Jon
You don't see any of the problems, do you. I've worked on TVs and video monitors for 40 years.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
How are you going to open the CRT's glass to add the plates, then pump it back down, first with a vacuum pump, followed by a diffusion pump. Don't forget to install new getter material to flash while you're inside the CRT.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
And hence the "tuned" nature of the deflection.
Exactly. As spelled out in my freshman electronics book in 1961.
Yes, they'd not only be too far apart (i.e. high drive voltages required) but they'd have too much capacitance (high capacitive currents required). You really need those electrodes inside the vacuum display tube.
--
Thanks,
- Win
Do they have to go inside?
Obviously the further apart, the higher the voltage required, and the dielectric constant of glass relative to air will change the field a little bit, so it may not be practical to put them outside. Also there might be a conductive coating on the inside or the outside?
Are there by any chance any moderately low voltage plates already in there for geometric correction or anything?
Of course while messing around inside the TV is fun, it's also hazardous. Here's an idea for something to do outside the box. Imagine a stable waveform being displayed on a triggered scope, with the horizontal sweep happening at about the same frequency as the horizontal scan rate of a TV. Now imagine the rastering TV beam sampling that frequency.
Seems that for this one horizontal frequency, you could build a box that had a ramp generator slaved to the vertical deflection, and a fast window comparator. When the window comparator says the ramp voltage corresponding to the current scan line equals the signal voltage at the currant scan X, you turn on the beam. In actuality you will be displaying a picture made up of one slice each of (#scanlines) periods of the waveform, but if both the waveform and your trigger circuit are stable, that's not a probem.
Obviously this is limited in the frequencies it can cover, but at least the vertical bandwidth is no longer limited by the coil inductance - instead it's limited only by what you can see on a screen with a comparatively low, fixed horizontal scan rate. Guess a multisync monitor would offer more options than a TV.
Typical deflection voltage is 300 VDC INSIDE the CRT.
Why would there be?
Obviously its a total waste of time. Find a surplus or used O-scope CRT to play with, instead. I've bought old tube type 100 KHz scopes for $2 to $30 at thrift stores and hamfests. Those worked. I've hauled home lots of dead scopes since the late '60s and fixed most of them with a handful of new resistors and caps, and sometimes a couple new tubes. You could fix most of them with a good VTVM and a schematic.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
A horizontal tv timebase is already running at well above audio. Although the fundamental is af, the harmonics needed to produce the waveform are multiples of this, so much higher frequency viewing should be quite workable.
A monitor that does high resolution and high frame rate will give all the more bandwidth, and colour.
NT
Blanking means switching the beam off to black while the scan coils whip it back across the screen, which takes longer than zero time. Dont worry about it, scopes work without blanking.
read your post again!
Simplest way to get it going is to take your stereo amp outputs, connect one channel to one scan coil, other to other. Voila.
When doing this, ensure that either:
I assume you know that a tv provides more death opportunities than any other household equipment, and that youre aware of them. If not, ask first, cos it can be a bit hard to ask after.
NT
Sounds like the elephant phenomenon, where you can look at the same thing from different perspectives and see something quite different.
NT
"An elephant is warm and squishy".
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Metal plates inside the tube, and huge deflection voltages. No, much too far away outside the tube, plus youd need excessive deflection voltages. Get it working now, look at weaks later.
But first, a few popular ways to die
- non-isolated supplies usually mean everything in the tv is live, including chassis, all electronics, speaker, etc.
- supply reservoir capacitor may store 160/330v for a long time after switch off.
- tube acts as capacitor to the 19-24 kV EHT. The thick red wire with black rubber cap is connected to this. Try not to get too close. Use care when shorting it out, and realise it will recharge itself after shorting, due to weird capacitance effcets, so it needs shorting 3 times.
- focus voltage may on some sets be a few thousand volts.
If the tv has as assortment of external connectors, it will be isolated from the mains. If it doesnt have these, its more likely to be non-isolated.
The big supply reservoir cap can be shorted out. There will often be more than one. If you want to keep the set working, short it using a low resistance rather than plain metal, to avoid damaging the capacitor.
Tube EHT stored can be shorted, but use a well insulated tool to do it, and ensure your shorting wire from screwdriver shaft to chassis and tube outer is securely attached, not just wapped round etc. Reason is if this comes loose you'll get bit. It is 24,000 volts, but the capacitance is small. People normally survive a bite from this, but not always. B&W sets are a lot friendlier in this area.
Focus can be shorted similarly. Focus connects to the tube base, its the well insulated one.
One last question for someone: how will the line output stage behave if its load is removed? You need that going to produce the EHT.
NT
I dont think the OP could. This is a fine opportunity to make something fun and learn lots. And end up with a basic scope.
NT
The concept of tv as oscilloscope is ludicrously absurd.
It was a standard classified ad scam of the 1950's.
TV sets use a very special and highly efficient fixed frequency recurrent phase locked horizontal scan. They cannot deviate far from
15,735 Hertz. Nor can they be randomly triggered.Use an A/D ahead of a personal computer instead. Or buy any of hundreds of stock pc oscilloscopeadd-ons.
Or pick up scopes surplus. A Tek 7904 should cost you $12 tops. A Tek 5440, they should pay YOU $12 to haul it away.
More details at
-- Many thanks, Don Lancaster voice phone: (928)428-4073 Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552 rss: http://www.tinaja.com/whtnu.xml email: don@tinaja.com Please visit my GURU\'s LAIR web site at http://www.tinaja.com
You could spend the time working with a real scope tube and end up with two useful things. A low end scope and your life. TV CRTs without the proper drive to the deflection coils have been known to develop a hotspot on the neck of the CRT and implode.
Zenith had to recall a whole year's worth of their early solid state TVS because of this. If the loading on the horizontal output stage changed the HV would rise and cause the tube to implode. I lost count of how many TV sets i personally modified with the new parts and applied the federally mandated safety sticker to the back of the cabinets.
Also, the glass at the neck of a TV or monitor CRT is thin and easily damaged. Have you ever been around a CRT that imploded? They have killed a number of people who happened to be in front of the tube.
It is dangerous to play with old CRTs when you don't know what you are doing.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
1 Old Commodore 64 or Atari 800 1 FPGA (lightly salted with VHDL or Verilog) 1 programmable clock generator with crystal 1 or 2 fast SRAM (optional, depending on FPGA) 1 fast ADC
Mix together on PCB or well-constructed breadboard, fold in the bitstream to the FPGA through a JTAG port, let stand while you prepare suitable firmware for the Commodore 64 or Atari. Burn firmware (or at least sear well on both sides) into game EPROM, insert RF modulator output into TV input.
Enjoy.
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
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