Page 18 - 2015-03

Power transformer Diode bridge rectifier Both resistors are 3 ohms.
All capacitors are 2200 microfarads

To amplifier
240 v
E

To lamp
The Eiki circuit (sorry, its hand drawn)

The low voltage secondary winding produced
4 volts. This high frequency voltage was ap-
plied to the exciter lamp. Being well above the
audio range it was inaudible and gave the same
results as pure DC on the lamp.
The proliferation of solid state components
(transistors, diodes, etc) in the 1960s made the
task a little easier. Left: The LUXEON high intensity LED
The type used in red light readers
The Eiki range of 16mm projectors incorporat-
ed a low voltage winding of about 8 volts on The later Bell & Howell projectors used a
the projector’s power transformer. It was fed power transistor as a series pass regulator, not
to a diode bridge rectifier and then to a series only filtering the DC applied to it, but regulat-
of resistor–capacitor filters and became the ing the voltage to the exciter as well. A similar
DC supply for the exciter. circuit is shown below.

Power * An AC sine wave has
transformer two excursions (positive
and negative) per cycle -
therefore the lamp gets
two ‘pulses’ of voltage
per cycle

4 volts to exciter

18 REEL DEALS March 2015