TV for oscilloscope

[Abstract Dissonance]

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.

Sure, and isn't this what the metal band that goes around them for?

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.

Well, I'm sure its dangerous to play with the mains, or nuclear radiation,
etc... but you gotta start somewhere. I think as long as you gotta enough
common sense and some luck then it should be ok. I'd rather play around and
take a 0.1% chance that it might kill me and learn something useful in the
process than be afraid to do anything(which I've always been when playing
with "high" voltage.. I've always only been comfortable with small
batteries... now I'm just starting to get used to it since I have variac
which lets me work my way up.).

--
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

Jon

 

[Abstract Dissonance]

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.

I think you are under the impression that I need a "fancy-smacy"
oscilliscope. I just need something to play around with for now. At this
point its more about just actually getting my "hands" dirty than anything
since several have pointed out I can get a cheap oscilloscope and the TV
isn't all that great.

Also, I assume you mean that are effective for that because the coils are
tuned to that frequency? Not because of the TV circuitry?

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.

I was thinking of getting on of those PC ones but not sure if they are all
that great?

One thing I don't like to do is buy stuff from ebay. Its just a huge scam
IMO or just to much trouble in the long run. Is there any other play to get
a cheap scope(but decent for a beginner) that is not an auction?

More details at http://www.tinaja.com/auct01.asp


--
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: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

Thanks,
Jon

 

[[email protected]]

AD,

You'll probably need a free soundcard oscilloscope like

http://polly.phys.msu.su/~zeld/oscill.html

to work your way through converting a TV.

Some repetitive waveforms can be converted down to 300-20,000 Hz using
a receiver with a BFO (beat-frequency oscillator).

Happy learning,

Steven

 

[[email protected]]

[email protected] wrote:

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.

TV tube safety has come a long way from then, to such a point that even
if the _front_ of a modern tube is broken its unlikely to im/explode in
a dangerous way. More to the point, since the risk is not zero, the
scope builder should be aware of what causes neck overheating, how it
can be a problem, and avoid causing the problem in the first place.
When deflection is excessive in a tv, or when the scan coils are too
far back, the e beam hits the neck of the tube and heats it up.

When using a tv tube as a scope, the total light output requirement is
a small fraction of that of it in tv mode, so the beam current will be
turned way down (if you want the tube to survive). This reduces the
threat. The OP should avoid using excessive brightness, and avoid
overscanning the tube. If your waveform goes off the edge of the
screen, turn the gain down or disconnect it.

As Michael says, if you ignore these points carelessly you could be in
trouble.


NT

 

[[email protected]]

Sure, and isn't this what the metal band that goes around them for?


Well, I'm sure its dangerous to play with the mains, or nuclear radiation,
etc... but you gotta start somewhere. I think as long as you gotta enough
common sense and some luck then it should be ok. I'd rather play around and
take a 0.1% chance that it might kill me and learn something useful in the
process than be afraid to do anything(which I've always been when playing
with "high" voltage.. I've always only been comfortable with small
batteries... now I'm just starting to get used to it since I have variac
which lets me work my way up.).

Variac outputs are usually connected direct to the mains, so its live
whatever the V_out setting.
..

NT

 

[[email protected]]

Sure, and isn't this what the metal band that goes around them for?


Well, I'm sure its dangerous to play with the mains, or nuclear radiation,
etc... but you gotta start somewhere. I think as long as you gotta enough
common sense and some luck then it should be ok. I'd rather play around and
take a 0.1% chance that it might kill me and learn something useful in the
process than be afraid to do anything(which I've always been when playing
with "high" voltage.. I've always only been comfortable with small
batteries... now I'm just starting to get used to it since I have variac
which lets me work my way up.).

Variac outputs are usually connected direct to the mains, so its live
whatever the V_out setting. Look up 'autotransformer'

 

[[email protected]]

AD,

You'll probably need a free soundcard oscilloscope like

http://polly.phys.msu.su/~zeld/oscill.html

to work your way through converting a TV.

Some repetitive waveforms can be converted down to 300-20,000 Hz using
a receiver with a BFO (beat-frequency oscillator).

Happy learning,

Steven

thats the one to use. Just put a buffer amp in front of your sound
card, as there is no input protection.

NT

 

[Michael A. Terrell]

Sure, and isn't this what the metal band that goes around them for?

The metal band around the front of the tube is to hold the mounting
brackets, and equalize the stresses on the tube as it heats and cools.
What does that have to do with the fragile neck?

Well, I'm sure its dangerous to play with the mains, or nuclear radiation,
etc... but you gotta start somewhere. I think as long as you gotta enough
common sense and some luck then it should be ok. I'd rather play around and
take a 0.1% chance that it might kill me and learn something useful in the
process than be afraid to do anything(which I've always been when playing
with "high" voltage.. I've always only been comfortable with small
batteries... now I'm just starting to get used to it since I have variac
which lets me work my way up.).

You need to study how a CRT works, if you think that a variac is all
that you need. Make sure that your will is in order and say good-bye to
your family while you still can. You appear to be pigheaded enough to
kill yourself. I've been around when a CRT imploded and pulled the
electron gun out of the wall on the other side of the room. I've seen
the glass and metal shards just miss a co-worker when a customer
installed color CRT exploded. He didn't have the tube mounted properly,
and had given up on setting the convergence on his bargain $29 rebuilt
CRT.

The chances of dying are a lot higher than .1% if you don't study the
safety issues first. Do yourself a HUGE favor and read the FAQ for
which is at: http://www.repairfaq.org/

--
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

 

[Joseph2k]

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

Such ignorance, i could hear badly designed tv horizontal deflection(15750
Hz, well below 20 kHz common boundary value) until my 40's, and could hear
18 kHz MGA horizontal in my early 30's. Of course proper oscilloscopes had
sweeps from 1 Hz to 100 MHz. TV's don't do that, they are designed fixed
frequency use.

 

[[email protected]]

[email protected] wrote:
Such ignorance, i could hear badly designed tv horizontal deflection(15750
Hz, well below 20 kHz common boundary value) until my 40's, and could hear
18 kHz MGA horizontal in my early 30's. Of course proper oscilloscopes had
sweeps from 1 Hz to 100 MHz. TV's don't do that, they are designed fixed
frequency use.

I see someone isnt thinking tonight. The a.f. timebase is not a sine
wave, it contains harmonics of several times the fundamental, ie the
scan coils can run at way above audio if need be. Doesnt imply the
scanning circuitry will, we wont be using that. Comprendi?


NT

 

[Don Lancaster]

Such ignorance, i could hear badly designed tv horizontal deflection(15750
Hz, well below 20 kHz common boundary value) until my 40's, and could hear
18 kHz MGA horizontal in my early 30's. Of course proper oscilloscopes had
sweeps from 1 Hz to 100 MHz. TV's don't do that, they are designed fixed
frequency use.

Not only fixed higher audio frequency, but that frequency is utterly
locked into the total energy budget for the entire television. Energy
goes into the horizontal scan only during the RIGHT HALF of the sweep.
It resonantly inverts and recycles for the LEFT HALF. Anything left over
sometimes becomes the B boost for vertical deflection and possibly
sound. Plus, of course, the high voltage for the CRT.

A true horizontal linear class A magnetic deflection on a larger tv
would take at least two or three kilowatts of line power. This energy
recycling was and remains positively brilliant.

Again, the "convert your tv into a giant oscilloscope" was a mainstay
outright scam of the classified ads of the 1950's. Which was before the
low end real oscilloscopes upgraded to triggered sweep and sweep delay.

--
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: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[Don Lancaster]

I see someone isnt thinking tonight. The a.f. timebase is not a sine
wave, it contains harmonics of several times the fundamental, ie the
scan coils can run at way above audio if need be. Doesnt imply the
scanning circuitry will, we wont be using that. Comprendi?


NT

Not even wrong.

--
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: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[Deefoo]

[crossposted to sci.electronics.design,sci.electronics.basics]

Anyone have any experience converting a TV into an oscilloscope?

Hmm... Saved the article in 1973 (Have no scanner and is not
in english),Title:Audioscoop.Coil resistance between 1.5 and
5 ohm.
They advice to put 10-15 ohm in series,to get a more linear
response.
You have to disconnect the line sweepback suppresion pulses,
or you will see a chopped wave.
I would advice to put your own voltage to that point, or
you will burnout the screen very quickly(or turn brightness
back to zero if possible).
Afer that, connect the coils to your stereo amplifier.
Other articles:
1962: Semi conducting diamont.
1969: Pneumatic logic gates(FF,OR,AND,halfadder,shiftreg.)
1970: Color tv with rgb lasers and mechanical rotating mirrors.
1970: Physical parameters measurments with Quartz crystals.
1966: Fuel cells.
etc. etc.......
Anybody have a nice operational timemachine??

Ha, ha, I remember another great project from the seventies (I think):
multiplexed tv, i.e. one tv that loops over several channels with viewers
wearing glasses with mechanical shutters synced to the channel scanner.
(BTW, it may now even be possible with lcd shutters...)

--DF

 

[[email protected]]

[email protected] wrote:

Not even wrong.

Are you saying the scan coils themselves are resonant? Ie on their own
without the drive circuitry. If not, what is preventing them being
driven with other frequencies?


NT

 

[[email protected]]

Recently used a monitor as a scope.
Two sets of isolated deflection coils Y deflection is more turns so
higher inductance and less current to deflect.
X coils lower inductan i.e needs higher current ie about _+1A for
deflection.
Gives great lissajou from audio etc.
More interesting if the signal drives colour as well or generates a
fiels to upset the colour alignment .
Try driving coils from stereo audio

 

[Don Lancaster]

Are you saying the scan coils themselves are resonant? Ie on their own
without the drive circuitry. If not, what is preventing them being
driven with other frequencies?


NT

No, I am saying that the horizontal scan coil does a hell of a lot of
other things besides horizontal sweep. The changing of whose frequency
TOTALLY TRASHES the ENTIRE operation of the rest of the tv set.



--
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: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[Rich Grise]

Are you saying the scan coils themselves are resonant? Ie on their own
without the drive circuitry. If not, what is preventing them being driven
with other frequencies?

The point I think some people are trying to make here about converting
an ordinary TV by just clipping the yoke leads and slapping on an amp
won't work.

The reason it won't work is that the coil's inductance is intricately
woven into the fundamental deflection circuit. And the horizontal is
even worse - it's right in the same circuit with the flyback - that's
where the name came from; that big spike when the flying spot flies
back to the other side to start another scan line. Cut the yoke,
and it won't oscillate, and you won't get any HV.

Now, admittedly, you could build a stand-alone flyback supply for all
of the HVs, and just throw away the vertical sweep osc, and then you
could drive the coils with current drivers, but yikes!

It'd be easier to get a used real scope at a ham fest for 5-10 bucks.
Even a fixer-upper - you'd get as much experience, and you know that
when it's fixed, it'll work!

Good Luck!
Rich

 

[Joseph2k]

I see someone isnt thinking tonight. The a.f. timebase is not a sine
wave, it contains harmonics of several times the fundamental, ie the
scan coils can run at way above audio if need be. Doesnt imply the
scanning circuitry will, we wont be using that. Comprendi?


NT

What part of "fixed frequency design" did you not understand? BTW what got
you to thinking that a proper sweep was anything other than a highly
asymmetrical triangle wave.

 

[Don Lancaster]

What part of "fixed frequency design" did you not understand? BTW what got
you to thinking that a proper sweep was anything other than a highly
asymmetrical triangle wave.

The input horizontal deflection coil sweep signal for a television set
consists of a SQUARE WAVE that lasts from center to right of scan.

--
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: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[Joseph2k]

The input horizontal deflection coil sweep signal for a television set
consists of a SQUARE WAVE that lasts from center to right of scan.

Don, you should know damn well that a "square wave" voltage into an
appropriate inductance plus a damper and a flyback results in a linear ramp
in current, which is what the magnetic field deflecting the electron beam
to sweep linearly at the design frequency.