26-10-2017, 04:26 PM
Hi Jeffrey.
Yes I'm on the NBTV forum but still feeling my way.
I hope to download or obtain some material.
This afternoon I altered the charging cap for the line blocking oscillator just to see if the timebase would run at an even slower rate without too much distress. I have found that I still get results at 1500Hz. the EHT goes down to 3kv though at this speed but decreasing the anode load of the ECL80 triode improves the sawtooth and its peak level, this had brought up the EHT to 5Kv and improved picture shape on 120 lines.
I had been feeding the Aurora from an old B&W camera pointing out of the shed toward the house as its been a nice sunny afternoon and I was quite impressed with the results on 240 & 180 lines, I inadvertently switched to 120 (mechanical) and lo and behold the line lock was reasonable, feeding it with video from a freeview box and its dreadful. I think the reason is the camera was set with the iris at its most closed point so the video level is low. I then tried 96, 90 & 60 and the set will resolve a picture down as far as this.
I'm even more gobsmacked that it's even possible.
I think now I'll need to use the mechanical sync output from the Aurora, I'll need to make a proper clipping circuit, most likely with a 555 timer to give me suitable synch pulses for the line oscillator and possible a divider circuit to trigger the frame. I'll need some form of line phase adjustment to square up the picture and I'd think if I can do this then as far as I can tell the frame should be triggered at the correct time. Of course each standard will require a different divider, nothing that's insurmountable though.
Yes I'm on the NBTV forum but still feeling my way.
I hope to download or obtain some material.
This afternoon I altered the charging cap for the line blocking oscillator just to see if the timebase would run at an even slower rate without too much distress. I have found that I still get results at 1500Hz. the EHT goes down to 3kv though at this speed but decreasing the anode load of the ECL80 triode improves the sawtooth and its peak level, this had brought up the EHT to 5Kv and improved picture shape on 120 lines.
I had been feeding the Aurora from an old B&W camera pointing out of the shed toward the house as its been a nice sunny afternoon and I was quite impressed with the results on 240 & 180 lines, I inadvertently switched to 120 (mechanical) and lo and behold the line lock was reasonable, feeding it with video from a freeview box and its dreadful. I think the reason is the camera was set with the iris at its most closed point so the video level is low. I then tried 96, 90 & 60 and the set will resolve a picture down as far as this.
I'm even more gobsmacked that it's even possible.
I think now I'll need to use the mechanical sync output from the Aurora, I'll need to make a proper clipping circuit, most likely with a 555 timer to give me suitable synch pulses for the line oscillator and possible a divider circuit to trigger the frame. I'll need some form of line phase adjustment to square up the picture and I'd think if I can do this then as far as I can tell the frame should be triggered at the correct time. Of course each standard will require a different divider, nothing that's insurmountable though.
