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Re: Small CRT Questions

"FyberOptic"

Hey folks. I came across a portable 5" B&W TV which has some minor > tuning problems, so I thought this could make a good platform to > finally experiment with controlling a CRT on my own. It might be fun > to try creating vector graphics and such from a microcontroller, or > rigging up a simple oscilloscope since I don't own one yet.
** First you need to realise that the " CRTs " used in TV sets are very different animals to the ones used in scopes.

TV set tubes are " picture tubes" and use very high voltages (10 to 25 kV) for beam acceleration and focusing and have NO internal plates for beam deflection. That is done with magnetic fields produced by coils mounted on the neck. They whole design is intended to produce a "raster" on the screen with hundreds of horizontal lines.

For playing around, you really need to get a small * scope tube * - the voltages used are far more manageable ( 500 to 1kV) and deflection is electrostatic and hence uses only low voltages and virtually zero current.

This page has some interesting circuits for very simple scopes:

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..... Phil

Reply to
Phil Allison
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Nice!

This was my first entry into electronics as a ~13 year old, trying to make a large black and white TV into such a "scope". It worked, sort of. Not very well of course due to the coil inductance. But I got a waveform displayed without killing myself.

--

John Devereux
Reply to
John Devereux

"John Devereux"

** Ha, ha !!!

I did the exact reverse at age 16.

Having built a very basic valve scope with a Philips 3 inch tube,

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I decided to connect it to the internals of my 17 inch B&W TV - after a few false starts and a few * sparks* I was very delighted to get a small green and black viewable pix.

I still have the same scope and it still works.

Got 5 more besides now.

..... Phil

Reply to
Phil Allison

You killed yourself without getting a waveform displayed?

I made something like that with a WWII (or maybe Korean war) surplus

3JP1. Still have a slight scar from the rather ample anode supply I made for it.

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Lovely little tube.

Not very pleasant watching shows in green and black, IIRC.

Reply to
Spehro Pefhany

[...]

I seem to recall, later on, hooking up a UHF tuner and a ramp generator to my (bought) scope, so as to get a tiny dim green unstable picture. Not sure exactly how I could have done that now, since there is no way I would have known how to make a sync separator. Must have used the scope TV trigger for H and manually "tuned" the ramp generate for V.

I've never made a valve circuit, looks quite fun now, from my older perspective.

--

John Devereux
Reply to
John Devereux

I used the video out from my old 'Panoramic' Spectrum analyzer to feed a scope to watch TV. I would set it for a slow sweep from 54 to

300 MHz, so it would pass through every channel on the cable TV feed at about one channel per second. It was fun to watch the 'dimbulb' types try to figure out what was going on. ;-) 
--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
Reply to
Michael A. Terrell

I still have an old Ball Hercules monochrome vector monitor. It went with my first 286, which was a cool Everex. The display was in a cardboard box. The one it shipped in. What I refer to is a bare tube with a nine pin D-sub soldered on to the end of some wires attached to it. I still have a few of the ISA monochrome adapter cards too.

Reply to
Pieyed Piper

Great company video here on how Tektronix used to make their own CRTs in-house.

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Best regards, Spehro Pefhany

--
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Reply to
Spehro Pefhany

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