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In Reply to: RE: new (to me) Russian PIO capacitor on ebay posted by Naz on August 05, 2013 at 20:48:04
Thanks, Naz.
Sounds like they should be "good enough" for use as bypass capacitors around electrolytic capacitors in the power supply for Beveridge direct-drive amplifiers, unless they get leaky at high voltages. Eight 450V electrolytics are connected in series across 3200V. I am thinking of bypassing each individual lytic in the string.
Follow Ups:
The K75s have very rich, fast, and dynamic mids...way superior in all ways to ANY electrolytic. I like them for power supply bypass duties. Yes, as others have posted, they can have a little high bandwidth edge to them, most noticeably in coupling duties (not so much with power supplies). I use them as final power supply caps, in larger values of course, as well as MBGO caps. Often I will use a high value MBGO in my power supplies, bypassed by a smaller K75. I've bread boarded supplies comparing electrolytics, MGBOs, Solen types, and motor runs. The best sound I could come up with, after MUCH experimentation, was the MBGO bypassed with a K75.
I've recently used 250V (50hz) 2.2uf K75-10 caps as parafeed caps in my 6n6p line stage (bypassed with .1uf SSG silver and micas), with excellent results. BTW, the way the Russians label caps, the voltage can be DC or AC rated. If it's AC rated, it will say 50hz, right after the voltage, so my 250V 50hz caps are good to about 350VDC (conservative). Yours look to be good to just their 630V rating, but that is more than the electrolytics.
Also the Rooskies are notorious for their conservative ratings, as most mil spec stuff was rated for use in severe duty environments, (high G, high vibration, extreme temperatures, and altitudes), so I doubt they will be stressed more than your 450V electrolytics.
I do admit that I never use components for more than their rated specs, but every time I've seen posts by folks that have, they seem to always report a very big tolerance for abuse, with Russian components in general. If I was you, I'd take the added precaution of wrapping the metal case of the K75s with several layers of electrical tape. After all, the series connection divides the voltage, across the string, but case to ground is a whole other story, 3200V gets into pretty scary territory.
twystd
Thanks for your thoughtful analysis and for the tip about insulating the cases. Good point.
Worth a try for the money.
Also, FWIW Mikey asked what my favourite Cap was but deleted the post. Since I went to the trouble of typing an answer but got side-tracked before submitting I thought I'd post it anyway. My answer:-
"I am VERY impressed with the latest V-Cap CuTF. These may be super expensive but almost impossible to fault and even better than the V-Cap TFTF and OIMP which I had previously used.
I've liked quite a few other caps for their particular strengths but few seem to be balanced overall. Of the Ruskies, Teflon and Silver Mica edge out PIO IMO, though you might throw a K40 into the mix to tame an edgy system.
Would like to try Duelund one day"
Naz
The KBGs and the OMBGs are fantastic but the Sonic Plats are my favorite of the commercial caps..They sound like a paper in oil mixed with a teflon but what I have really found is putting paper in oil caps where B+ is present and putting a film cap or teflon where B+ is not present.The best cap I have ever heard are the Russian silver mica but you have to stack them as they only come in .1uf.THey are so neutral that you really aren't listening to a cap.
I cant justify spending the big busks on the latest and greatest boutique caps after I found those puppies.
twystd
"This the first pair of Mc30s I did with this cap arrangement..You see a soniccap plat on the input,a single K40y going into the phase inverter,but on the most critical stage you see the silver micas,which are going from the phase inverter to the voltage amp.From the voltage to the driver we have gudeman pios.Three months ago I changed out the last caps to SSGs also but I only stacked two of the .13s which put us right where we wanted to be.I have to find the photos.
You may have to do what I did on my Acoustat servos as I converted those 6K6gs..Your amp uses 36KD6s and I as I remember,the filaments may be in parallel. Rodger Madjewski designed them and they are very nice amps but getting the tubes is like pulling teeth.
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