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reply to Larry Gibb's ? of



                      Subject:                              Time:  11:37 AM
  OFFICE MEMO         reply to Larry Gibb's ? of Mar95      Date:  5/17/95

Larry,
Your question was what could effect Rank resolution aside from electrical and
optical focus.  I can only speak from my own experiences so here goes.
1.  Astigmatism must be set carefully to have the spot as symmetrical as
possible.  The H and V Resolution wedges should both come into maximum
electrical focus at the same time to test for this. 
2.  Beam Alignment, done during CRT installation, if not correct, can
compromise res.
3.  The type of CRT can also effect res.  Some CRT's can have a smaller spot
size than others.  
4.  I understand that Dave Walker's Digital Deflection system allows for a
smaller spot size due to the Focus Coil being replaced by a unit with superior
Electromagnetic Lens.  Haven't seen this for myself, maybe someone who has
this can confirm or deny.
5.  Beam Current will theoretically effect res.  This usually only becomes a
problem as the CRT aproaches end of life and the gun can no longer emit a
focused beam at higher beam settings.  We always run at 300 micro amps and do
not have a problem with res. at the present time.
6.  Color Channel frequency response should be flat to at least 8 MHz then
roll off above that.  The type of Afterglow boards you are using will also
effect frequency response.  I prefer to use the older type 100807's with built
in H-aperture correction not the 100807d's with the tunable cap as the high
freq peaker.  Updating the R and C values on the 807's for better Afterglow
Correction is also very important as well as adding another R/C timeconstant
to fill in the gaps on the Fourier Aproximation of the Afterglow Correction.
7.  Aside from the above, the Digiscan 4 also has frequency tweeks in side of
it but I think these only effect the analog RGB output so if your path is 601
to the Encoder, tweeking these will have no effect.
More noise on the internet from Dave Corbitt