Quote:
Originally Posted by Chris K
OK. I'm still trying to understand this. You said what I'm measuring on the VTVM is residual 21.25 MHz signal voltage??? Then there's -120V DC in addition that goes to CRT? I guess I need to know more about how this circuit works and what it does. I'm in uncharted  waters. At R119 (or around R119 as I'm looking at the schematic) there's a -120 volt demodulated video signal that goes into the video amp. Along with it, there's residual 21.25 MHz voltage that needs to be "tuned out" by adjustment of T-103? The residual voltage would cause an issue with the demodulated signal going into the amplifier tube??? Or am I WAY off base? |
Look at it this way. This set is designed to include a two stage DC coupled video amplifier. Let's go back to basics: why is there a two stage DC coupled amplifier? Next to provide the two stage DC amplifier, the two stages have to be DC stacked. With regards to the cathode and control grid, the plate is roughly at +120vdc. So to DC couple the two stages, the first stage grid/cathode is at about -120vdc, the plate of the first stage is DC coupled to the second stage grid/ cathose at around 0vdc and the plate of the second stage is coupled to the grid of the picture tube at around +120vdc. This is to couple the DC component. Do you understand this?