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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.
Follow Ups:
Caps are just another tool in your voicing tool box, just like the different types of resistors. Each has their own sound and it's mix and match until you get the sound you want. Simple, but it can take a lot of trial and error. I have some 500v K42Y's in a preamp and they were just the ticket because it had been too bright and in your face for my taste. They smoothed it out nicely. On another amp I tried them and with the other parts I had in there they were too dull. I put in some russkie teflons and they were just right. It all about the over all package.
Last summer, I completely rebuilt a pair of MkIIIs for my brother's use, using Roy Mottram's VTA circuit. I used a single .1uF / 1000V K40Y9 between the first stage voltage amplifier and the phase inverter and used Auricaps between the inverter and the output tubes (KT90s). All parts were hand-selected: a combination of PRP metal film resistors and Riken carbon films. The power supply is all polypropylene.These amplifiers are driving a pair of KEF 104/2s and sound great. I got the exact balance I was looking for between accuracy and warmth. They put out between 70-80W each before clipping.
I frankly don't care for the way stock MkIIIs sound at all, but I love them as the basis for a rebuild.
I don't understand. First you make a component change based on tweak buzz around here that doesn't work out for you. Life is learning. Then you make another change based on your own experiences and exclaim "Bingo! Relaxed, powerful sound with a wide and balanced bass." Sound to me like you achieved what you wanted in the first place. Great! But then you lament: "So here I sit still waiting to experience the sound of a good (and reliable) PIO cap." Why not enjoy what you've got now? You've already determined that PIO caps probably won't satisfy you for a couple of very good reasons.While I respect Mike's opinion, I've found that most PIO caps are flawed in many ways and therefore I won't use them in anything I intend to use routinely. The last thing I want to intrude into the listening experience are distracting thoughts like "Have I gotten the last 0.01% out of equipment?" or most importantly "I wonder if the coupling caps are going to fail in the middle of the music taking out the output tubes, OPT and rectifier. Life is too short.
Hi Jack:If you have the patience... try bypassing the oil with say a point O one (.01) RTX (or other small value cap)...
it's a try it and listen proposition... if it works... bingo... if not go back to the full size RTX.
Caps are like seasonings--- you really have to experiment to find the right tastes.
let us know--- I was surprised a bit that the K40's didn't work at all for you.
cheers,
Yes Mike
thats has worked for some people..I do that in my other loudspeakers and I actually use a poly bypassed with a pio..SSDP.
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