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Video Amplifier Question
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Return to top of page · Post #: 1 · Written at 4:23:04 PM on 19 March 2016.
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Location: Silver City WI, US
Member since 10 May 2013 Member #: 1340 Postcount: 977 |
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I am unsure of the reason they connect a 2μF capacitor from cathode to screen on this early RCA TV  |
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Return to top of page · Post #: 2 · Written at 10:13:21 AM on 24 March 2016.
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Location: Beechmont, QLD
Member since 10 April 2009 Member #: 465 Postcount: 109 |
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That is so the valve acts as a pentode, by fixing the screen, as far as the signal is concerned, to the cathode potential. This valve is used as both a common cathode amplifier, for the chrominance signal, and a cathode follower, for the luminance signal. |
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Return to top of page · Post #: 3 · Written at 2:33:01 PM on 24 March 2016.
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Location: Silver City WI, US
Member since 10 May 2013 Member #: 1340 Postcount: 977 |
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Why not just use the 2μF capacitor to decouple the screen (to ground)? Would it not work just as well? |
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Return to top of page · Post #: 4 · Written at 12:29:01 PM on 4 April 2016.
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Location: Silver City WI, US
Member since 10 May 2013 Member #: 1340 Postcount: 977 |
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One way to observe the effect of signal connection from cathode to screen would be to remove detector diode and feed the amplifier a Multiburst test signal: then monitor the output at the plate of the 2nd video stage (serving as a buffer stage for this purpose). Then jump out the chroma trap for "flat" response. Then note any difference in gain or response when the 2μF is removed, or grounded. Although Multiburst test signal generators are hard to come by (only used for testing broadcast systems). |
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