1. Home
  2. Electronics Design
  3. Re: Question of TV technology, if anyone can answer two questions

Re: Question of TV technology, if anyone can answer two questions

And further, the other question, why don't they use electrostatic

> deflection? At least for the horizontal. I am pretty sure that > today's transistors would have alot of trouble doing 1080i, if they > ever can at all, because the yoke is inductive. Start kicking H up to > 67.2 kHz, it is no fun. But with a non-inductive load, wouldn't the > scan rate changes be easier to manage? They do it in spades in > scopes.

Using electrostatic deflection requires a CRT with deflection plates. Such a tube would have (I believe) a thicker neck. Also, the output transistors would have to swing at least a couple hundred volts to deflect the beam.

My guess is that Sony, et al, stick with magnetically deflected tubes because they've been the standard for 60 years. That's the kind of tube they build, and the kind of deflection circuits they design.

However "correct" your theories might or might not be, they run up against industry practice. Electrostatic deflection is considered obsolete, at least with respect to video displays. And pretty soon CRTs will be obsolete with respect to video displays.

I have a Toshiba CZ-3299K HDTV that's about 12 years old. It has a 32" magnetically deflected CRT, and runs at four times the normal scanning rate (~ 63kHz) without problems.

Electrostatic deflection might be more affected by beam current > changes.

I don't think so. Try changing the screen brightness of a 'scope's CRT. Does the deflection change?

I do not know enough CRT technology to know something of that > nature. However, they have already found out that steady deflection > along with precise HV regulation does not work. The raster will get > smaller because beam density affects deflection sensitivity.

Again, I don't think so. If this were true, the image on any magnetically deflected CRT would show severe geometric distortion that varied with image brightness. It doesn't.

That's why there are seperate resistors going to each CRT anode in a > high voltage splitter. That is also why they have abandoned extremely > tight HV regulation in favor of more precise and modulated control of the > deflection. They have integrated HV level with beam current, and also > use it to control the vertical drive now.

Are you sure? How can you change beam current without changing brightness?

Reply to
William Sommerwerck
Loading thread data ...

Electrostatic deflection can be much faster, but the focusing properties are much worse. Electron microscopes all use magnetic focusing and magnetic deflection for that reason--you can't get any sort of decent spot size with electrostatic. For analogue oscilloscopes, the spot size hardly matters--1mm is fine--but that's not true for TVs.

Cheers,

Phil Hobbs

Reply to
Phil Hobbs

And they use narrow deflection angles, infeasible in a TV. The problem would only be worse with wider angles.

Reply to
Clifford Heath

Such a

Actually, it's not too bad. At a paltry 1800V acceleration, the tube in my Heathkit IO-103 gets pretty well 10V/cm, which is at least a 60V supply for its window. Focus works just fine at this voltage, as sharp as my Tek. It's beyond me why they designed the deflection circuits for 150 and 180V supplies.

Tim

-- Deep Fryer: A very philosophical monk. Website @

formatting link

Reply to
Tim Williams

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.