K40Y-9 630V, USSR PIO audio capacitors. One of the best Paper in OIL capacitors made in the Soviet Union, smooth, natural and harmoniouslys sound. Excellent performance in controlling guitar tone, tube amps, Hi-Fi tube amps and studio equipment.
A separate description deserves the "armor-piercing" design of paper / foil K40U-9. It seems that these capacitors should work in a nuclear explosion, in a word, these capacitors were originally originally produced for Soviet Army equipment.
It is noteworthy that for K40Y-9 capacitors, the loss tangent decreases with decreasing signal level and reaches for Dx = 0.0005, which has a favorable effect on the sound.
I will choose for you a matched pair or a quad for coke.