TV line selector

[ppppenguin]

The monostable turned out to be rather critical. The original 5n cap was very temperature stable so I replaced it wih a 4n7 polystyrene. After a few attempts to adjust values on test I resorted to fitting a 5K preset pot in series with the 15K resistor. The range over which is works for both 405 and 625 is very small but there seems to be some overlap.

I'll fit a lower value pot as it's right up at the low resistance end. If I'm not happy I'll have to drill the case and fit a 405/625 switch.