New Vista/Philco

[old_tv_nut]

Originally Posted by nasadowsk

Ok, shouldn't a higher HV be less of a burden to the flyback because he shunt regulator's not holding it down as much?

The HV regulator works by sampling the total current in the HV suppply, and keeping that current constant. Based on the equivalent resistance of the HV supply, setting a particular total current will set a particular voltage. So far, you have it right - a higher voltage means there is less (constant) current draw.

1) if you go too far towards low current and higher voltage, you will run out of range and out of regulation on bright pictures sooner. This is more of an issue with sets that have full DC coupling (which no early roundies had).

2) running insulation beyond its rated voltage is asking for leakage and eventual breakdown

So, higher voltage setting is probably easier on the horizontal output tube, but harder on the flyback.

My opinion is to follow the specified setting, unless you are willing to gamble.

[kx250rider]

Originally Posted by old_tv_nut

2) running insulation beyond its rated voltage is asking for leakage and eventual breakdown

So, higher voltage setting is probably easier on the horizontal output tube, but harder on the flyback.

My opinion is to follow the specified setting, unless you are willing to gamble.

My concern exactly. Thanks for the detail on that. It's the higher voltages, closer to the failure point of the insulation of the windings, that causes the arc-over and burnout of the FBT.

Charles

[DaveWM]

Good to know, thanks for the input.

[old_tv_nut]

Second on checking the HO current. Agree it's a common cause of overheating the flyback and more likely to kill it quickly than any other cause.

Horizontal circuits are designed very close to actual planned usage due to the difficulty of handling high currents and voltages. Flyback transformers are a balancing act between staying within the safe limits of the horizontal output device, producing the desired output, having suitable fire-retardant properties (which affects the dielectric constant, distributed capacitance, and dissipation factor of the winding), etc. etc.