b. Assuming 40kvp has been selected, a low positive voltage is on lead MVH
into pin 2 of IC9 resulting in a low negative voltage at pin 6. This low negative voltage
being input to the 747 op-amp at pin 7 is less negative than the set-point voltage at pin
6. The output at pin 10 will be a low negative voltage and space charge compensation
is some portion of that low negative voltage as adjusted by pot P30. By selecting a
higher kv (now assuming 78kvp) at IC9, pin 2 becomes more positive, driving pin 6
more negative. On pin 7 of the 747 op-amp, this more negative voltage equals the set-
point voltage on pin 6 and pin 10 becomes zero volts. There will be no
c. As the selected kvp increases (now assuming 110kvp) at IC9 pin 2 there is a
higher positive voltage, and pin 6 becomes even more negative. This more negative
voltage comes to pin 7 of the 747 op-amp increasing the differential between pin 7 and
the set-point voltage at pin 6 causing the output at pin 10 to be proportionally positive.
The space charge compensation will be a portion of that positive voltage as adjusted by
potentiometer P30. The space-charge compensation voltage goes to the filament circuit
via lead XCM to modify the filament-drive voltage.
FILAMENT SELECTION, CIRCUIT FUNCTION DESCRIPTION 3.2
Refer to figure 2-6. On lead XCN is a negative (-) 15vdc voltage which is
regulated to negative (-) 8vdc by the 7908 voltage regulator. This voltage is used to
supply all parts of the filament-selection circuit and the final result on lead XDA ma set
will be some portion of that negative (-) 8vdc. Each ma selection is made by closing a
set of normally open relay contacts which selects a series of potentiometers for the
coarse ma, fine ma, and added filament-boost adjustments. These pots modify the
negative (-) 8vdc as necessary to produce the selected ma. Potentiometers P1 through
P8 are the coarse-ma adjustments, P11 through P18 are the fine-ma adjustments, and
P21 through P28 are the added filament-boost adjustments for each ma station.
Potentiometers P9, P19, and P29 are not used.
a. For discussion purposes assume the 100L-ma selection has been made by
depressing the 100L-ma-select push button. Normally open relay contacts XD1/XA5
are now closed and, because of the 100kΩ pull-up resistor, a high comes to pin 1 of
IC8. IC8 is a 4532B 8-bit priority encoder. The output is the binary code for the
respective input. If more than one input is high simultaneously, the one with the highest
number will be encoded while the other input will be ignored. In this discussion with the
100L-ma station selected, pin 1, which is input 4, is high. The output of IC8 will be pin
6, which is the Q4 output, and it is a high to pin 9 of ICs 5 and 6.