Quote:
Originally Posted by Penthode
...The white line would be the result of the transition when the HO Tube conducts. If the HO Tube does not begin to conduct before the recovered energy is fully dispelled, the sweep will be momentarily halted resulting in a vertical drive line. Increasing the horizontal drive beyond a certain point will cause the HO Tube to remain cut off longer hence the conduction will not pickup in time resulting in the line.
|
I wish we had someone very familiar with the details of HO tube operation. For instance (figures for 6CD6), I do not know why the maximum rated peak cathode current (700 ma)and maximum rated average cathode current (200 ma) are different. I also do not know why the peak plate voltage (7000 volts) is only allowed for 15% of the horizontal period. In transistor circuits, it was common to make the retrace time longer (and the pulse wider) specifically to reduce the peak voltage, which was much more critical to the transistor specs than pulse width. In fact, IIRC, some CRTs were narrower than 4x3, so the shorter trace time would not produce fat people.
Was something gained by keeping the tube HO drive on-time to the minimum necessary? Lower G2 dissipation? Lower average cathode current? Could the design-center on-time simply be increased and thereby avoid the limit-tolerance cases where it wasn't enough? I don't know.