T3D (Mostly OT) Projector lamp substitutions/modifcations]

[Rob <lilindn@xxxxxxxxxxx>]

     I am in search of some information in the seemingly slight
differences in the vast number of different types of projector lamps. 
Usually, each manufacturer would assign a unique three-letter code to
its own bulbs, to force consumers to use their bulbs for replacement,
and any information on substitution was kept in the dark.  The situation
is completely different from that of vacuum tubes used in radios and TV
sets, where a tube substitution manual was an important tool in every
serviceman's tool box.
     From what I understand, it is usually (always?) OK to substitute a
bulb of the same filament location, base wiring and base orientation if
the substitution is equal or "downward"  (e.g. - a 500 watt CZX is fine
for the TDC 716 - designed for the 750 watt DDB, a 400 watt DAT is not
only compatible for a 500 watt DAK - 400 watt DAT bulbs are now marked
"DAT/DAK").
      Some bulbs are identical to others with the exception of an
internal reflector behind the filament.  Obviously, using a bulb without
an internal reflector in a projector with a black plastic wall behind
tghe bulb will cause problems, but, a bulb with an internal reflector
can sometimes be used in a projector with its own reflector - my
Airequipt Superba 77 (2D), has marked on the bottom that it can use the
CZA (has reflector) or DAK (has none), among others.  As an experiment,
I tried a CAL (300 W, internal reflector) in an old Sears (Sawyer clone)
designed for DAK (500 W, no reflector).  It worked fine, no vignetting,
ran very cool.  From this, I get the inpression that the CAL could be a
substitute for an enormous variety of bulbs.
    This brings me to the Realist 620  - AKA Ansco Dualex, a medium
format projector that can show 35mm or even Realist stereo slides (in 2D
of 1/2 of the pair) with adapters.  A pair of these projectors may be a
resonably inexpensive was to experiment with medium-format
dual-projector stereo projection.  They also use a horizontal-burn bulb
called a DGA that has been out of production for some time.      
Immediately, the DEK (used in many Kodak Carousels and therefore quite
common) came to mind as a possible substitute (they are both horizontal
burn with the same physical and electrical base, though the the DEK is
500 W versus 300 for the DGA, and the DEK has an internal reflector
whereas the DGA has none).  I placed the DEK in the 620's socket, only
to find that the internal reflector is on the wrong side of the
filament!  It came to mind to turn around the socket inside the
projector to right the internal reflector, but then the grid placed on
one support post (it's on all horizontal-burn bulbs - anyone out there
know what it does??), would be under the filament instead of over it
(could that cause a problem?)  This would be an "upward" substitution,
of course, which would produce other problems with the heat (would
changing the fan to a more powerful one suffice?)
    Thanks to all in advance.
    Rob
    "Everything I have is Y1.96K compliant"