|
Nederlands Forum over Oude Radio's |
Re: De afmetingen van de kathodestraalbuis zijn begrensd...
Geschreven door Henk Roovers op 15. Apr 2006 12:52:34:
In reactie op: Re: De afmetingen van de kathodestraalbuis zijn begrensd... geschreven door anton tan op 15. Apr 2006 12:23:13:
Ho Anton
niet zo hard van stapel lopen. We zitten wat die metalen buizen betreft in de jaren vijftig hoor! De hele televisie was nog niet uitontwikkeld. Als je de televisie uit de jaren net na de oorlog vergelijkt met de huidige exemplaren, dan is onderhand alleen het principe van overdracht gelijk gebleven. Zelfs tot voor kort was de televisie nog volop in ontwikkeling. Neem nou een simpele electronenbuis. Hoe zagen de eerste powerpenthodes eruit voor commercieel massagebruik en vergelijk die eens met een van de laatst ontwikkelde buizen voor tv, zoals de PL519. Zelfs de anode had een speciale vorm, om de electronen de goede richting op te sturen en bijverschijnselen te onderdrukken. Zelfs in de oorlog was men daar al mee bezig en dat leidde tot de uitvnding van de BEAM-POWER terodes, zoals bijv 807.
Op het www vond ik trouwens nog iets over de constructie van een trinitron. Het is geschreven door iemand bij Philips, maar ik neem aan dat ook hij weet waar hij over schreef.
************************************************************************
Comparison of CRT Types"Could someone please help to elucidate the comparative advantages of each technology? I know how they work but do not know which is advantageous and why."
(From: Jeroen Stessen (Jeroen.Stessen@philips.com).)
Trinitron is Sony technology. The aperture grille (which performs the function of a shadow mask in Trinitron and clone CRTs) consists of vertical wires under tension. The mask is always straight in the vertical direction and curved in the horizontal direction, thus the shape is a cylinder. The tube surface is also cylindrical, which causes some strange effects, particularly funny mirror reflections of yourself. Because the wires are under a lot of tension, the internal tube structure must be very strong and thus relatively heavy. Because the glass surface is cylindrical instead of spherical, the glass must be thicker and heavier too, to withstand atmospheric pressure.
Heavier always equates to more expensive!
The electron gun construction is also different: there are still 3 guns (not one as some may think but the 3 guns share one main lens. (The assembly of focusing grids is called a lens, in analogy to the optical principle.) There are still 3 cathodes and 3 G1s, as usual. The large diameter lens has the advantage of less spherical aberration (and thus a sharper spot) but the disadvantage of large physical length which means a deeper cabinet.
In the deflection coil design another compromise is found between spot quality, purity and convergence. As a result horizontal convergence must be helped by an auxiliary dynamic convergence waveform (on an extra convergence coil?). This adds to cost and can occasionally give an interesting failure of the horizontal convergence.
The best non-Trinitron (or clone) CRTs use a conventional shadow mask made of Invar - originally Matsushita technology; Philips uses it too. The shadow mask is of the standard shape (spherical metal plate with holes in it) but it is made of a special alloy with a 7 times lower coefficient of thermal expansion than regular iron. This allows a brighter picture with less purity errors.
The problem with regular shadow masks is 'doming'. Due to the inherent principle of shadow masks, 2/3 or more of all beam energy is dissipated in the mask. Where static bright objects are displayed, it heats up several hundred degrees. This causes thermal expansion, with local warping of the mask. The holes in the mask move to a different place and the projections of the electron beams will land on the wrong colours: purity errors. The use of invar allows about 3 times more beam current for the same purity errors. See the section: What is Doming?.
Combating purity errors is a necessity due to 2 trends:
* Flatter picture tubes: flatter shadow masks are more sensitive to doming
* Darker (glass) picture tubes: this gives more contrast but more beam current is needed for enough brightness
The trinitron aperture grill is inherently insensitive to doming as long as the tension in the wires remains positive. If the wires become too long then they become more sensitive to microphony (try tap the cabinet...). The vertical wires are connected in several places by thin horizontal wires. Some people complain about seeing faint shadows of these wires.
To summarize: Trinitron monitors are probably heavier, larger, more expensive, maybe better on purity, and maybe better on focus than other monitors, with or without invar shadow masks. There are excellent monitors other than Trinitron too... I suppose the Coke-Pepsi comparison is true.
*********************************************************
Dus kennelijk toch drie kathodes
mvg Henk Roovers
- Re: De afmetingen van de kathodestraalbuis zijn begrensd... Henk Roovers 15.4.2006 12:56 (4)
- Stalen beeldbuis (artikel) Ed van der Weele 15.4.2006 14:53 (1)
- Re: Stalen beeldbuis (artikel) Henk Roovers 15.4.2006 15:27 (0)
- Re: De afmetingen van de kathodestraalbuis zijn begrensd... Henk Roovers 15.4.2006 13:56 (0)
- Re: De afmetingen van de kathodestraalbuis zijn begrensd... Henk Roovers 15.4.2006 13:55 (0)