wrote:

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I want to replace the original capacitor which is located across the AC
power line in a Zenith Trans Oceanic (tube radio). The original cap is a
.047 at 600V (standard capacitor). I was told that these days, standard
caps are no longer used across the AC power line. Instead, they use
these Radial X2-AC Safety Capacitors.



** The use of 600V DC rated caps across a 120VAC supply line is time honoured and normally perfectly OK - long as you are not in a high lightning area..

The issue that arose was in 240VA counties when wax impregnated paper caps were replaced with plastic film types. Some of these would last only weeks before developing internal shorts and exploding.

The problem was soon found to be due to tiny pockets of air trapped inside the cap when being wound - corona discharge developed across these pockets and destroyed the cap. However, such corona currents did not normally occur with 120VAC so US makers kept using plastic film types.

The fix for 240VAC places was to use two 600V film caps is series, thereby limiting the effective voltage to 120VA for each. Cap makers in the UK and elsewhere developed a method of winding "two in series" film caps as a single part and these became standard for class X caps.



..... Phil