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K40y-9 PIO Caps - My Experiences

Posted by sayntjack (A) on February 25, 2007 at 10:15:07

Following the many good things I had read in AA about the K40y caps I managed to score 10 0.22uF, 1000V units on e-bay from a Russian block vendor. The transaction was smooth and tests with my cap meter and 600V leakage tester showed no issues. I went for the 1000 Volt units because after trying the 630 Volt Jensen PIO I ended up throwing them all in the garbage because of leakage causing bias upset in my Dynaco MkIII. I had bought these for a 2nd set of Mark IIIs I was modifying (both with Triode El. driver board, SDS cap board basically - the 1st was my reference the 2nd was for experimentation).

From the onset the sound of the MkIIIs with the K40y in the output tube input position was restricted (constipated)and the bass was boomey - almost seemed to be resonant at one frequency. Believing that the problem was break-in issues I ran the amps for 3 evenings at 3 hours each, then after no improvement and refusing to believe that the caps were at fault I began rolling tubes in all locations and gave it a few more evenings - all with little change and a big disappointment in comparison to my other very satisying sounding Mark IIIs running Multicap RTX coupling caps. In frustration I ripped out the K40y and stuck in 0.22uf, 600V Multicap PPFXS. Bingo! Relaxed, powerful sound with a wide and balanced bass. I really was quite suprised at the transition and have no idea why the K40y were so dismal especially when others have had such good luck. I know Mike Samra sure likes 'em. So here I sit still waiting to experience the sound of a good (and reliable) PIO cap.

Jack

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