Philco 50T-1401 Ion Trap & Low Contrast

[wa2ise]

Originally Posted by bonanzaman

.just turn the brightness control all the way down before shutting the set off......no bright spot! duh!

You can do a similar thing automatically by connecting an electroytic cap between B+ and the brightness line, if the brightness changes the voltage on the G1 of the CRT. When you turn the set off, the charge in the cap will push the brightness negative as the B+ supply collapses, thus pushing it negative, cutting off the emissions of the CRT cathode. Thus no or greatly reduced spot.

[bonanzaman]

Originally Posted by wa2ise

You can do a similar thing automatically by connecting an electroytic cap between B+ and the brightness line, if the brightness changes the voltage on the G1 of the CRT. When you turn the set off, the charge in the cap will push the brightness negative as the B+ supply collapses, thus pushing it negative, cutting off the emissions of the CRT cathode. Thus no or greatly reduced spot.

That would be a great to add feature for the set; looking at the schematic, the center wiper of the brightness control goes directly through a 100k resistor to
the cathode of the 12LP4, so not sure if that would work, however.