Genius 1793, ISO XFR-75W, 2093, 1493, 2793 Video Amplifier Schematic, NE592, Blue Video Amplifier

940 .

VIDEO AMPLIFIER SCHEMATIC.

127V

.1uF

957

Blue Video Amplifier 937

18

3

16V

120V

560 Ω

MPS2907

75Ω

13

2

+12V

10

12.1K

K17

950

K13

1.49K

K15

17

301Ω

18 Ω

14

K9

40.2K

Ω

K14

K2

140

2SA

15

.1uF

K16

MMBT

K19

1370

250V

16

887

3904

951

7

19

9.25V

BLUE

K34

1

10

.015uF

VIDEO

7

10

180Ω

3

885

TO

Dark screen

SOT

20

K18

CRT.

Ω

80-110VDC

606

1.0K

NE592

3

1nF

K7

K8

K32

150Ω

205Ω

PART

Jumper

8

956

12

2SC

OF

14

.5W

953

FDH400

K3

3467

AUTO

K33

5

.1uF

4

BIAS

943

958

1N4148

MPS2907

1.8K

7

2SA

100Ω

K36

3pF

934

33Ω

8

6

15

Ω

955

Beam

1370

K21

K20

K4

Current

1

681Ω

A

5.62K

945

9

11

1.8K

Feedback

	K6			K11			954 948	FROM
	1N4148	21K	836Ω		2.2K	3.32K
1.62K							BIAS CONTROL LINE	CA3224
K1	K35	K22	K10	5 9 12	K5	K12		GND
					GND
+12V								+12V
						1.8K	9.25V
							MPS A64
VIDEO INTERFACE						938
			VERTICAL and				D 942
	MG		HORIZONTAL
						3.92K	.1uF
			BLANKING,
			Master Gain, &			940	930
			Beam limiter				GND

R

G

B

VIDEO SOURCE (external)

The bias current of the push-pull output

stage is set by resistors

,

,

,

K14

K15

K16

, and diode connected

transistor

.

K17

950

Transistor

is thermally connected

to

950

transistor

to maintain the same base to

951

emitter voltage drop. Note that resistor K17 adds 11mA to the diode connected transistor

950. This current is available to drive the base of transistor 951 during periods of high frequency amplification. This high base current is needed because, the beta of transistor 951 is low for high current pulses and when high frequency is amplified many high current pulses occur. The mechanism for transferring the current from

transistor 950 to the base of transistor 951 is the coupling capacitor 885 which charges through resistor K16 on the positive part of the signal and discharges through the base of transistor 951 on the negative part of the drive signal. Therefore the output stage, bias current, is frequency dependent and has a range of 3mA to 15mA.

Resistor K13 and capacitor 887 , which are connected to the 9.25 volt line, decouples the video amplifier current pulses from the 127V line. The 9.25 volt line is connected to the emitter of the NPN push-pull transistor by resistor K4 . This voltage establishes the output voltage of the NE592 in the middle of it's ±2 volt drive range. The 9.25 volt line is regulated by darlington transistor 942 with voltage divider resistors 938 &

69