2115_ Gee_MkII_Tropical.pdf - VMARSmanuals

MAIN TIME BASE
STROBE .TIME BASE
-
----- ----- c.
BIAS VOLTAGE
4-h
BLACKOUT
TRACE
(A) MODULATOR GRlD POTENTIAL WlTH
COMPLETE 0. C. RESTORATION
--
STATIC
------- - ------
BIAS VOLTAGE
-
(B) C.R.T. GRID POTENTIAL WlTH
NO D.C. RESTORATION
"ft
- ------ ------------.--------.--------I----
If
STATIC
BIAS VOLTAGE
(c) C.R.T. GRlD POTENTIAL WITH
PARTIAL D.C. RESTORATiON
Fig. 39.-D.C. restoration. Indicating anit.
9
P
C
Flyback blackout.
of the negative-going pulse. That is, the
83. Blackout pulses for the cathode trace brightness would depend on the
ray tube are taken from the suppressor magnitude and width of the blackout
grid of V5 through the condenser C13. pulse.
On the strobe time base position, positive 85. Now in the strobe time base position,
pulses are applied to the _erid of the C.R.T. the blackout pulse to the cathode ray tube
to brighten up the tube durins the trace, is of much longer duration than in the
whilst on the main time base the negative main time base position (see fig. 39). Therepulse
on the suppressor blacks out the tube fore, with V19 omitted, the positive grid
during flyback- The diode, V19, d-c. re- potential during the trace would be much
stores at the grid of the cathode ray tube. higher for the strobe time base than for the
The d.~. restoring action is made slightly main time base ; so much higher in fact
inefficient by means of the resistance R32 that the strobe time base would appear
in series with the diode : this tends to equalise brighter than the main time base in spite
the brightness between the main and strobe of its increased speed of scan.
time bases.
86. Suppose now that complete d.c.
84. The action of the diode V19 and R32 restoration were attempted, that is, V19 were
may be explained as follows. If V19 connected in circuit but R32 were short
were omitted from the circuit (i.e. no d.c. circuited. In this case, because of the
restoration were attempted) the mean pot- unidirectional conductivity. of the diode
ential of the grid of the cathode ray tube the grid could not rise above earth potential
would be zero or, in other words, during and hence the potential during scanning
the time when no pulses were being received would always be zero. It would follow
from the suppressor ,of V5 the potential therefore that the higher speed strobe
of the grid would be positiwe by an amount time base would be less bright than the main -
dependent on the magnitude and width time base.
.