While working on my Philco 48-700, the .4uf 3500v HV filter capacitor shorted and started smoking. Can I use a film capacitor in its place? Any ideas where to purchase an equivalent would be appreciated.

Thanks in advance

Yes film should work fine. You may need to do series pair of 2KV .82uF.
Mouser doesn't have anything close to .4uF at over 3KV... Digikey might.

Possibly something like this, all I could find that was in stock:

https://www.digikey.com/en/products/detail/kemet/C4BSYBX3470ZBMJ/7400087?s=N4IgjCBcpgTAnAZiqAxlAZgQwDYGcBTAGhAHsoBt EWRANltgA4QTYxEwAWCEsR2AAwB2AKwgAuiQAOAFyggAyjIBOA SwB2AcxABfVgM7wUIdJGz5iZSiAEA6EQAIArQDEWN250bO3JO5 yEfd39OIL9PR1dgz0Qwj244-yDJEFl5AFV1VRkAeQwAWQIsPABXZQJdEgBaWGNTFRLLckgqMXE dDqA

All I could find that was close, If the voltage rating is insufficient you may need to special order something.

Possibly something like this, all I could find that was in stock:

https://www.digikey.com/en/products/detail/kemet/C4BSYBX3470ZBMJ/7400087?s=N4IgjCBcpgTAnAZiqAxlAZgQwDYGcBTAGhAHsoBt EWRANltgA4QTYxEwAWCEsR2AAwB2AKwgAuiQAOAFyggAyjIBOA SwB2AcxABfVgM7wUIdJGz5iZSiAEA6EQAIArQDEWN250bO3JO5 yEfd39OIL9PR1dgz0Qwj244-yDJEFl5AFV1VRkAeQwAWQIsPABXZQJdEgBaWGNTFRLLckgqMXE dDqA

All I could find that was close, If the voltage rating is insufficient you may need to special order something.

would a Snubber cap work in such a situation?

Be aware this set has the extremely dangerous “brute force” high voltage supply. They are known to kill!

Be aware this set has the extremely dangerous “brute force” high voltage supply. They are known to kill!

I have never worked on such thing before, so I'm not sure so thus i brought attention to it.

"In modern power electronics, they are commonly found to reduce ringing. A snubber circuit limits or stops (snubs) switching voltage amplitude and its rate of rise, therefore reducing power dissipation."


VS what Electronic M mentioned, using 2 series pair of 2KV .82uF.

bandersentv has done this many times, and would know the most about it.

Another possibility, cheap (but a minor nuicsance to construct).

Replace the chain of resistors from the 0.5 uF cap to ground with
a chain of (mostly) 200 volt 1.3 to 2w Zener diodes, with one different voltage to get the
drop across the focus pot right. Then you can use a bunch of 630 volt caps
at say 0.1 or 0.27 uF across triples of Zeners. Because the voltage is regulated, you
would only need a lower capacitance to filter out the Zener noise.

I've used such Zener chains in a couple of TVs and they work fine. Of course
you have to figure out how to construct them.