TELE-TECH & - AmericanRadioHistory.Com

\- SECONDARY
ELECTRONS
GUN
ENLARGED CROSS- SECTION
OF SCREEN
IU
ANODE BUT TUN
30 KV
SCREEN BUTTON
27 KV
Fig. 1: Apple tube and monochrome tube arc similar in size and appearance
Fig. 2: Secondary emission from index material generates index signal
Single -Gun dolor TV System
Philco's "Apple" system uses single electron beam to excite vertical color
phosphor stripes. Beam current is modulated by transmitted color video signal
and self -generated index signal which indicates the location of the beam.
IN conventional color TV display
systems, either each of several
color phosphors is excited by its
own electron beam while protected
from the other beams by mechanical
or electrical means, or, alternately,
a single electron beam is
directed to several color phosphors
by electromechanical or electrical
means. The Apple System, described
here, uses a single electron
beam to excite vertical color phosphor
stripes. The beam, instead of
being forced to land on a particular
phosphor, is passed over all color
phosphors in rapid succession and
modulated, in accordance with its
position on the face of the tube, to
produce the required color.
The beam current is controlled
by 2 signals: the color video signal
from the transmitter, and a self -
generated index signal which indicates
the location of the beam. The
only circuitry unique to the system
is that required to perform these
functions.
aluminized background, and placed
behind every red stripe on the face
of the tube. (See Fig. 2). The secondary
emission current, produced
as the beam crosses the index
stripe, is collected, amplified, and
heterodyned, resulting in a signal
of the same frequency as that at
which the writing beam is varied
to produce colors.
The variations in the writing
beam that produce colors also produce
an ac component of the secondary
emission current at the
same frequency as the desired index
signal, and at any phase to it.
Since this ac disturbs the desired
index phase, a second beam of low
current, the pilot beam, is generated
from the same gun as the
Fig. 3: Complete Apple receiver. Circuits in dashed lines follow conventional color receiver
practice
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Index Signal
The index signal is obtained from
the tube structure itself from a line
of "index material," having high
secondary emission compared to the
INDEX
AMP
SIZE DISCRIMINATOR
4
98 Tele -Tech & ELECTRONIC INDUSTRIES June 1956