In the Pultec passive filter, the caps must be able to take 10V.
And all the caps should be "film" (or oiled paper, but that's very old-tech).
The thinnest plastic film can take 50V, and many types are not offered in any less than 250V or even 600V.
Get the right value of capacitance, and a size/shape which fits. Be sure it is rated for more than 10V, actually 50V.... if you are looking at "16V", it is probably an Electrolytic which is cheaper but not the best choice for a passive EQ.