The convenience of one of AO's original illuminators should not be diminished. They fit snugly into their intended ports and are easy to use under the stage with the transillumination base for transmitted illumination and DF.They can be moved into almost an infinite number of positions in order to gain the correct lighting angle and the nose of the lens system is small, so they can be fitted into tight situations. They provide a focused beam. They are actually, quite a neat system. Using the basic physical design and improving their illumination characteristics seems preferable to the boyscout approach.
If you unscrew the two screws that fasten the lens section from the base, you can slip out the reflector and install a light blue filter over the collecting lens. Any size from 25mm to 35mm will do, because the filter rests in a little relief created by the sides of the reflector. Small filters may rattle a little but they cannot fall out of place. This solves the colour temperature problem of the tungsten filament .
AO made a dual transformer for those lamps, being fully aware that the standard 18 watt bulb was a little dim, yet serviceable for classroom situations where lower magnifications might be implicated. More professional set ups used two illuminators, which can be driven from the one model K 1991 transformer or two single transformers. The K 1991 transformer has dual on offs and dual variable intensity settings for critical cross illumination adjustment. I have one and even with the 18 watt tungsten bulbs it is a joy to use.
In lieu of having a dual transformer, an option is to use the one illuminator in it's overhead port and another of the type fitted to a scissors adjustment on the transformer; a so-called nicholas illuminator. In this way , one can illuminate with varying degrees of shadowing, in various directions simply by moving the second illuminator around and slight reorientation of the sample. If one wants almost completely shadowless lighting, that can be accomplished too.
Tungsten illuminators work quite well when used by a qualified user and when properly set up.
AO had three of those basic external illuminators with the ability to articulate into desirable positions for stereoscopic microscopy. They also had several flexible halogen/fiber optic units and fluorescent ring illuminators. I also like the halogen fiber optic system but not the fluorescent ring illuminators.
I have retrofitted a couple of the external tungsten illuminators to led with varying degrees of satisfaction. Firstly led illumination alone, does not give the best results. Tungsten or Halogen plus led I found to be best, so two illuminators are needed. Secondly, the tungsten bulbs used in the three Nicholas type illuminators are all different. The older Cyclospot uses a GE 1497, the starlight( like the one you have jb89) uses a GE 1460 and the Universal uses a GE 1493. The former two a dual pin bulb and the latter uses a single pin bulb with a grounded base.
The GE 1493 used in the Universal can be directly replaced with one of these
https://www.ebay.com/itm/2pcs-set-6V-24 ... SwtYRdwTzW. The lamp is cooler but the intensity a little less. It is also a very stark brilliant white with a slight blue cast. It works well, when coupled to a halogen or tungsten aux. lamp as well. I have used it in an older self illuminated DF condenser, which originally had a 14 watt tungsten lamp and it works pretty good there.
The other two bulbs have a ground pin and a line pin. The only real difference between them , is that the Cyclospot has a two pin push and turn car type bulb and the other has a locking ring type bulb. Otherwise the actual bulb is the same; a 17.88 watt with a short tight focused tungsten filament.In order to "upgrade" one of these to led, a two pin option needs to be found and in the case of the # 1460, the locking ring needs to be desoldered from a dead bulb and soldered to the base of a replacement....if one can be found.
A possible option for an led replacement for the 1460 bulb I have found is an led 6v. motorcycle headlamp. With this type of lamp the base is the ground , and each pin is the line for the high or low beam. I have one enroute, which I hope to be able to disassemble and rewire so both the high and low go to one pin and the ground is removed from the base to the other pin. There is even a version with a metal flange that conceivably could used to replace the locking flange on the 1460 bulb. We'll see how it goes. Not sure what wattage equivalent these will be but I would think around 35 and the housing of the illuminator may also turn out to lack enough ventilation to prevent the electronics of the bulb from overheating. There is the aluminum reflector, which might work as enough of a heat sink.
https://www.ebay.com/itm/1-x-P36D-Motor ... Sw3F5dw~G9