Buffer Capacitors in Car Radios and other Equipment

What is a buffer capacitor?

 It is a high voltage capacitor across a vibrator transformer secondary in a radio and is designed to reduce the voltage spike across the transformer.

It is important to replace it with the correct factory value. They can be anything from .001 to .1 mfd. Typically in the .001-.006 range; and 1000-2500VDC rating. There is a high pulse across this buffer capacitor, so value and voltage are important.

If your radio has a missing buffer capacitor or you suspect the wrong value was installed? Here is how to determine the correct value:

Hook up power to the radio and insert an ammeter in the + line to the radio. Then with a capacitor in place, check the current draw. You can substitute other values until the current draw is at it's minimum. That is the correct value to use.

It was always recommended by the radio manufacturers that when replacing a vibrator you replace the buffer capacitor, as a bad one will cause the vibrator to fail early in service.

(I know of one shop owner who would supply anything value wise he had for the buffer "Just put this in, it will work". Not a proper repair for the customer. Yes it would work, with very early vibrator failure resulting, and possible transformer damage also.  He also put in the cheapest "no name" capacitors he could find. Not my idea of an honest, or competent repair "tech").

Sprague and other companies actually made a specific "Buffer Capacitor" series and they labeled the capacitors "Buffer" right on them. Just replace the capacitor to insure long vibrator live, as these days vibrators are a high dollar item. 

If you are unable to determine the correct voltage for the missing buffer, and have no access to service data, I would suggest using 2500 volt or 2KV rated capacitor. Now the originals were paper/foil type and the Mylar film are a great substitute. I do not recommend using ceramic or mica types.