Replacing a Polystyrene Capacitor

[cparsons2391]

I am working on an Admiral 13in portable tv from 1968-69. It uses mostly Polystyrene clear capacitors. I am needing to replace one that looks bad and beat up. It is in the Horizontal AFC circuit. It comes off of pin 6 on the 8LT8.

It is capacitor C48 on the schematic below. The value is .0039 500v.

My question is can I use a film capacitor or do I need to use another Polystyrene or Mica?

Thanks!

[ppppenguin]

If they used 0.0039u (3900pF, 3.9nF) then I presume they wanted a fairly close tolerance. Otherwise they would have used the more common 3300p or 4700p. I would use any decent quality film capacitor.

I can't see a need for 500V rating though the schematic isn't entirely clear. Film caps are commonly available at 400V, sometimes 630V. IMO the 400V part will be fine.

Finally, if it's value is still correct and it doesn't leak then it doesn't need replacing. Even if it looks a bit rough.

[old_tv_nut]

It is a part of the pulse shaping, not part of the oscillator itself, so the temperature coefficient will not be critical. Just need the same voltage rating and 5% tolerance.

Edit: agree that 400V film is probably fine.