A bit of progress, not much, but some. I have to decide on which CRT method of doing video modulation I am going to use, cathode or grid?
So I am going to put down my thoughts here as a way of getting feedback, and basically trying to get it correct in my grey matter.
WRT Volts, the grid is negative to the cathode, so positive going video (-sync) will brighten the screen on video peaks. Negative going video (+sync) applied to the cathode will brighten the screen on negative peaks. At this point I am working on using the grid for video input and varying the cathode to provide fixed brightness.
Not knowing how much voltage swing I need from black to white I am making an assumption of 50 Volts maximum.
The plan using a DG7-5 CRT is to have the final anode at +HT of 230 Volts, which means that the cathode is down at around -600 Volts, this as it is relatively easy to use a voltage doubler from the mains transformer secondary to provide this negative volts using the normal HT to provide the 800 to 900 Volts required for the tube. It also means that the deflection plates are within the normal HT range approx 200 Volts. The down side is a separate 6.3 Volt heater winding for the CRT.
I have issues which I am not getting through, one is DC restoration of the video as it has to be in the -600 Volt area, the second frame flyback suppression, using the screen grid from the frame miller timebase as a blanking pulse to drive the CRT grid when that is the video input?
Anyway this is the circuit diagram to date.
personnalTV.pdf (Size: 90.25 KB / Downloads: 2)
Adrian
Also on UKVRRR
So I am going to put down my thoughts here as a way of getting feedback, and basically trying to get it correct in my grey matter.
WRT Volts, the grid is negative to the cathode, so positive going video (-sync) will brighten the screen on video peaks. Negative going video (+sync) applied to the cathode will brighten the screen on negative peaks. At this point I am working on using the grid for video input and varying the cathode to provide fixed brightness.
Not knowing how much voltage swing I need from black to white I am making an assumption of 50 Volts maximum.
The plan using a DG7-5 CRT is to have the final anode at +HT of 230 Volts, which means that the cathode is down at around -600 Volts, this as it is relatively easy to use a voltage doubler from the mains transformer secondary to provide this negative volts using the normal HT to provide the 800 to 900 Volts required for the tube. It also means that the deflection plates are within the normal HT range approx 200 Volts. The down side is a separate 6.3 Volt heater winding for the CRT.
I have issues which I am not getting through, one is DC restoration of the video as it has to be in the -600 Volt area, the second frame flyback suppression, using the screen grid from the frame miller timebase as a blanking pulse to drive the CRT grid when that is the video input?
Anyway this is the circuit diagram to date.
personnalTV.pdf (Size: 90.25 KB / Downloads: 2)
Adrian
Also on UKVRRR
Learning as I go!
Youtube EF91 Valve
Youtube EF91 Valve
