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Re: Thick face plates



At 10:52 PM 4/25/95 -0700, Julius Friede wrote:
>Does anybody have any opinions regarding the thick face plate tubes on 3C's=
?


Yes. In general they seem to be a *good thing* for the following reasons:

1. Low flare characteristics which were considered to be an early plus for=
 the URSA when it first appeared on the scene.

2. Crapola on the tube face is placed way outside the focal plane of the=
 gate and thus contributes a slight shading error rather than a well=
 focussed blotch followed by an inverse afterimage caused by the parallax=
 error between the light emission at the phosphor and pickup of the tube=
 dirt by the burn cell.

3. The positive electrostatic charge which would tend to accumulate on the=
 outside face of the thin face CRT, and hence attract further dirt, seems to=
 be minimised on the thick faceplate tube.

4. We no longer need a tube blower to constantly blow ionised air over the=
 CRT face ( if you know anyone who wants to buy these from Editel, let me kn=
ow!)

5. The phosphor appears to be set back further from the 45 degree mirror,=
 necessitating a larger patch for the same scanned area on the film, and=
 therefore less apparent tube grain. ( The same effect can be gained by=
 moving a std. tube back in the cradle). I leave the drawbacks of the larger=
 patch to be explained by the folks who use Metaspeed (try running at 100fps=
 to see what I mean).

Possible drawbacks are:

1. Separation of the faceplate glass button from the rest of the CRT, on=
 tubes manufactured in this fashion. (Rob L. and I had this happen with a TE=
 tube in the middle of a session a year or so ago!)

2. Lack of flare "coma" around the CRT spot could tend to exaggerate tube=
 phosphor grain, i.e. the result of the spot having a smaller half-amplitude=
 width.

3. Reduced light output. Anyone at Brimar, Tube Enhancements or New Century=
 care to give us exact comparison figures on this?

4. Theoretically some dispersion of the light could occur ( i.e. the glass=
 acting like a prism and smearing the spot into its spectral components). I=
 have no evidence of this, but include it to be contentious.

Hope this gives you food for thought. Feedback, especially argumentative,=
 welcome from other readers :-)=20