Excellent Russian PIO capacitors for a wide range of applications. Depending from capacity and voltage, can be used as coupling (interstage) capacitors, by-pass (shunt) caps, or guitar tone capacitors (for example most popular K40Y-9 400V / 0.022uF).
According to Soviet tradition, they are copies of the Bumblebee capacitors, the dielectric is Paper in Oil. By mine humble observations this is the best audio capacitors, which were produced in USSR. In ratio price / quality, veterans such as SPRAGUE VITAMIN Q, or Orange Drop are far behind. So, if you ask me about K40Y-9 as Vitamin Q I choose Socialistic K40 instead of Capitalistic Vitamin).
Also, we have K40Y-9B edition (red caps), which have a more reliable insulation of the case and reduce efforts to avoid electrical reduction, especially through their use as a parallel cap for electrolytic caps under the printed circuit board. By my customers feedback, K40Y-9B has a more interesting sound than the regular silver K40Y-9.
So, if you are looking for a replacement capacitor for a guitar amp (or a cover for your Gibson Les Paul), you should try this Russian PIO capacitors. The capacity tolerance is the weak point of these capacitors, but for a few pennys I get the matched pairs of quads for you as 0, XXYZuF. For example - you are looking for a K40Y-9 400V 0.047uF. I choose them as 0.0472uF= in the range of 5% from nominal capacity, also as close as i can closest ESR (equivalent series resistance).
Summing up this Russian review of capacitors, i can say that whatever you were looking for PIO capacitors, for guitar, power source, or cathode by-pass capacitor, I can say, that K40Y-9 is the best Russian PIO capacitor.