14-09-2018, 06:59 PM
Hi.
Well this afternoon I decided to see what I could do regarding the frame timebase. If you remember I previously made up a board for driving a scope with a 555 timer for frame, sync separator and video drive. I utilised the 555 for a frame sawtooth. Obviously the 555 signal was too low to drive the scan coils. I tried various combinations with and without an output transformer, although I could scan the tube the drive waveform was way wrong, I'm sure all down to the fact I don't have a suitable matching transformer. The best circuit was using a directly coupled FET to a NPN transistor feeding to an output TX. I I'm now considering using an IC output capacitively coupled to the scan coils or using a chip with balanced positive and negative supplies driven from the sawtooth from the 555. If I can get this running I'll concentrate on the line stage.
The pictures show the cobbled up work so far with the labpack running on low mains to feed CRT heaters (22v range) and focus volts from the DC HT connections, the labpack is fed via the variac at a very low setting.
Well this afternoon I decided to see what I could do regarding the frame timebase. If you remember I previously made up a board for driving a scope with a 555 timer for frame, sync separator and video drive. I utilised the 555 for a frame sawtooth. Obviously the 555 signal was too low to drive the scan coils. I tried various combinations with and without an output transformer, although I could scan the tube the drive waveform was way wrong, I'm sure all down to the fact I don't have a suitable matching transformer. The best circuit was using a directly coupled FET to a NPN transistor feeding to an output TX. I I'm now considering using an IC output capacitively coupled to the scan coils or using a chip with balanced positive and negative supplies driven from the sawtooth from the 555. If I can get this running I'll concentrate on the line stage.
The pictures show the cobbled up work so far with the labpack running on low mains to feed CRT heaters (22v range) and focus volts from the DC HT connections, the labpack is fed via the variac at a very low setting.
