Ten-Tec TITAN III 417, Руководство пользователя

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5-4
5.4 SCREEN SUPPLY AND GRID BIAS BOARD A10 (81950) This board contains the
screen supply, grid bias supply, and protective circuits for the 4CX800As. The screen
voltage is rectified by diodes D4 – D7 and filtered by C1 – C3 and C15. This DC voltage is
then regulated by pass element Q8. Load resistors R25 – R27 provide a current drain to
insure screen current remains in the positive direction. MOV Z1 protects the power supply in
the event of tube arc and insures the screen voltage can’t surge above 450 VDC. R23
provides a voltage drop proportional to the screen current to drive the front panel screen
current meter.
Grid bias voltage is rectified by D13, then filtered by C10. Q1 senses the key condition
and via Q2 and Q4 switches zener diodes D2, D8 and D16 in during key down and out during
key up. This zeners the bias voltage to approximately –55 VDC during TX and –100 VDC in
RX. Due to differences in tubes, J21 allows adjustment of grid bias in 4 settings:
-47V Pins 1 and 3 shorted
-55V Pins 2 and 3 shorted
-60V Pins 1 and 2 shorted
-68V no pins shorted
This adjustment is factory set to match the tubes shipped with the amp. If the tubes are ever
replaced, the jumper setting should be selected to produce approximately 200 – 400 mA of
plate current when keyed with no drive. The circuitry of Q7 senses grid current and begins to
fold back grid bias toward cutoff as grid power approaches 2 watts. Zener diode D1 provides
regulation for the negative 16 VDC power supply to run the meter circuits on the meter
switch board and the relay hot-shot circuit on the SWR board.
FIGURE 5-5 SCREEN SUPPLY BOARD (ASSEMBLY A10)
COMPONENT LAYOUT TOP VIEW