Philco 48-2500 Restoration Blog

[John Folsom]

I would think it is not the focus coil current that needs to be controlled, rather the HV needs to be regulated. As the As these supplied to be rather anemic, I would think a shunt regulator would not function all that well. But it would be interesting to try it . Or, as the Philco HV supply is independent of the horizontal sweep, it should be possible to build a feedback design which compares the HV to a reference voltage and used the difference to drive an amplifier to modulate the screen grid voltage on the horizontal output drive to the flyback, or modulate the B+ voltage to the flyback. Either approach would be interesting to try.