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C3 du e to the higher cha rging voltage .
Transformers T3 and T4 in th e video
circuit can be changed to a plate-to-pushpull-grids
( 1:2 rati o) in terstaged transformer
since brea kdown voltage no lo nger
is a critical factor.
v,
v,
Fig. 1. Radar de flection yo k e.
~
,W
UK 22K
Fig. 2. Coils must be mounted on CR T and the
CR T m ust bave th e same post accelerator voltage
as your monitor will supply .
Th e input to the deflection circuit
should be at the junction of the 27 kn
resistors in the cat hode circuit of V7 .
The 200n wirewound balance control
should be set so that nearl y equal curren ts
are drawn by each tube. This can be
determined easies t by temporarily adjusting
the bias controls for maximum resistan
ce, grou nding th e grid s, and remo ving
screen voltage. Then adjust the contro l to
approximately equa l voltage on the cat h­
od e.
Th e 500 kn bias con trols should be set
by feeding a 15 Hz signal into th e amplifiers
and putt ing a scope on the catho des
of t he ou tput tubes. (On the 15 liz
amplifier one end of the catho de by pass
has to be removed temporarily .) Adju st th e
bias co ntrol for the best sawtooth wave
forms on the scope. Since the vertical
signal is practically d c (.07 5 Hz), the 15 Hz
signal will have to be tem porarily used in
making the bias adjustments for the vertical
deflection amp lifier. Slight balancing
can be mad e with the bias controls, if
required , as long as the waveform doesn't
chang e too much.
If a 5 in. tube is used it may be
necessary to increase the scre en resistor to
lower the sweep of the unit, or a 100 kn
2W pot cou ld be wired in if a gain co ntro l
is desired . If a larger CRT is used it will be
necessary to increase plate voltage and
per haps change tub es, dep ending on how
much defl ection is needed . Keep in mind
that if a larger CRT is used it must have
approx ima tely a 55-degree defl ect ion
angle.
The high voltage req uired for the elect
rostatic CRTs can be eliminated , although
a 4 to 8 kV (depending on CRT) po sta ccelera
tor rf supply will have to be built. An
alternate circuit for the - 120V line in th e
monitor is shown. Th e rf supp ly is fairl y
str aightforward ; C I and LI are resonant at
approximately 15.750 kHz. Almost any
horizontal ou tput tube can be used for V3 .
For a 5FP7 only 4 k V is needed so the
booster diode can be eliminated. If greater
than 8 k V is needed for the CRT it may be
necessary to put some inductance in
(where the T V set's deflection coils were
connec te d) to make up for not co nnecting
the TV set's deflection coils, or if this
doesn't help, a voltage doubler can be used .
Ju st add another 2-turn link for th e filament
of the other recti fier.
Th e new volt age divider string for most
magnetic deflection tubes is sho wn in Fig.
3 and needs no explanation. The .01 pF
capacitor is co nnect ed to t he grid of V I to
supply vertical retrace blanking, and can be
mov ed to the plate of V2 if more blanking
is required. If this capacitor is connecte d to
the grid of V I , a 60 0V unit will do well;
otherwise, a 3 k V unit will be need ed
because of the inductive kick of the deflection
coil when the ver tical sync pu lse
comes.
For focusing of the CRT a perman ent
magn et unit with a centering con tro l would
48
73 MA GAZIN E