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Nikon Labophot Microscope

Introduced around the same time as the Optiphot (1978), the Labophot is lower cost and less flexible.
Positioned for labs rather than research, many were configured for phase contrast.

Nikon 221403 Labophot Microscope Parts Only (S1084)

eBay item number: 155061301918
Condition: For parts or not working
Manufacturer: Nikon
Nikon 221403 Labophot Microscope Parts Only (S1084) "No power."

Received 11 July 2022
Base casting broken next to illuminator;
potentiometer broken.

LED conversion

Common (grounded) emitter bipolar transistors are approximately constant current sources.
Labophot and Optiphot use transistors to modulate halogen lamp power
and variable resistors between base and collector for control.
Labophot potentiometers are about 1K Ohms, connected between collector and base,
with halogen lamp between collector and nominal +7 VDC,
to accommodate incandescent lamp behavior:
LEDs behave differently:
Francisco made an LED replacement similar to my intent:

To power a 5W LED instead of 20W halogen,
replace 1K variable resistor between 2N3716 collector and base,
which supplies a minimum of 1mA forward bias,
rewiring the potentiometer as a voltage divider with:
  • 680 Ohms in series between CW and +Vcc (about 8VDC),
  • wiper to base, and
  • CCW to -Vcc