Burned out High Voltage Capacitor
Capacitors aren't usually rated in Amps, but there is a upper current limit due to dissipation with the internal ESR (equivalent series resistance).

First, replacing something rated for 24 A with something rated for 4 A without knowing anything else is a stupid thing to do.  Burning out the component, starting a fire, or vanishing into a greasy black mushroom cloud should all be expected outcomes.

Second, do the math.  What current will flow thru the cap at what frequency?  Your schematic doesn't show what kind of tube V1 is, nor the values of the plate resistors, so there is little more that anyone can help with here.  From those values, you could get a upper bound on the current thru the cap.

Since this is apparently a RF oscillator, you also have to check that the cap still acts like a cap at the intended frequency, which you also haven't stated.  No real capacitor is perfect, and all real capacitors have a upper frequency bound on their operation.  Electrolytic caps are especially poor at this.  The schematic shows the cap being polarized, so it is probably electrolytic.