CIRCUIT DESCRIPTION
1.VIDEO AMPLIFIER
The Fig. 3 details the cascade video amplifier. Video amplification is provided by the TR303 and TR304. TR303 and TR304 are connected in a cascade configuration. TR303 operates as a common emitter and TR304 operates in the common base configuration. This minimized the miller effect input capacitance and the difining breakdown parameter for TR303 which becomes BVCBO as opposed to BVCEO.
This enables selection of a higher speed/lower breakdown transistor to be used in the video amplifier.
The emitter of TR304 is driven by the collector of TR303 which is a high frequency transistor. Overall voltage gain for the stage is determined by the ratio of R312 to R316. Bandwidth is within 3dB to 32 MHz.
2.POWER SUPPLY
The 120V AC line voltage is applied to the primary of the T901 where it is stepped down through the secondary winding to approximately 17V (AC). After passing through the bridge rectifier circuit and filter (C905) the regulated DC supply voltage is approximately 18V (DC). The 18V unregulated B+ voltage is applied directly to the collector of the B+ regulator (TR901). A voltage divider network (R905, VR901, R906) in which the B+ adjustment control (VR901) is used to establish the desired operating level (12V DC). When AC input voltage variations occur, a correction voltage is produced at the base of TR903 and is coupled directly to the base of the error amplifier (TR902). This correction voltage is then passed from the emitter of TR902 directly to the base of TR901 and B+ voltage regulation is then accomplished.
R314
TO@ < ;
+
c305
lOOuF/‘16V
T R 3 0 4 KTC2229
R316 L301
1.ZK/ZW 4.7uH
• TO v
70
+
2~ C308 2.2uFll oov
• TO CRT CA.THODE
R317
3 3 0
3 T R 3 0 3
TO @
2N3904
R309
7 5C306 12OP
R313
4 7
Figure 3, Video Ampllfler
