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Large Oil Capacitors

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Gentlemen ~ I would appreciate a little advice please

I would like to Cull the electrolytics out from a couple of Mullard 5-20's and have been mulling over the ASC Oil/Poly cans .

I was wondering whether anyone has any experience with these as I am looking to replace the 16uf+16uf 450v electrolytic with pairs of 20uf ASC's if I can shoehorn the bugger's in !

Tvm .
I have been using ASC motor runs and I really like them.

A bit "slower", I was told, but it seems to sound better than electrolytics that I have tried (Nichicons and Nippon Chem).

I use them on my tubed amps and preamps.

The only thing I hate about them is too much real estate that they occupy for small capacitance they provide. :D
I have also been using ACS motor run caps in my power supplies. They have been working well. I have not used them in any other position in an amp yet (bypass, coupling).

If there is a drawback it is their size. I've drilled holes in my top plates and let them project through, mounting from underneath with mounting clamps.
The biggest disadvantage is that when the paper-caps are wound they are pressed into a more oval shape. This pressing introduces pockets of air in the capacitor which gives a high degree of distortion, making paper-in-oil caps absolutely unusable for audioapplications, though they are very hype now.
In a PSU they may work, but remember that a PiO-cap also has a very high degree of tgd (tan delta or loss factor) compared to plastic caps.
A capacitor winding is wound round. Then it is sintered and at the moment the winding is mechanically pressed into an oval shape. Connections are solded to the ends of the wound cap and put in a can and filled with oil.

The process when the cap is sintered gives "holes" between layers in the the winding and these holes causes odd harmonic distortion.

A plastic (polyprop) cap is sintered using heat that makes the plastic shring and tightening the wound cap, closing in any cavitities.

And I repeat, using a PiO in a PSU is OK I guess but using it in signal routes is definitely not recommended.
ASCs are available round, filled with mineral oil and sound great as parafeed output caps in a headphone amp. Disadvantages are size, leakage capacitance between the lead and the metal case and a much lower self-resonance point than an equivalent hi-perf electrolytic, the latter most important in a PS application.

Re: oval caps, I don't agree. The best sounding in the above headphone amp, including electro's, Solens and ASCs, were massive 15 year old 660 volt GE Dielectrol oval oil caps.
I'ld be interested in the resuts. One of my personal undefendable voodoos is that - at a sufficient distance from the fundamental - jiggery-pokery down there counts. Maybe it helps these particular caps were burned in at 208 volts for 8 years doing power factor correction duty at the bottom of a 14kW on-line UPS. :)
I was working at RIFA capacitor plant in Kalmar, Sweden for almost 10 years with this bloke. I spent the last years calibrating all electrical instruments and he helped the technical dept develop/test new cap types.
We played around with metal foil/polyprop caps that we sintered (high temp, long time) very hard making them extremely dense and mechanical stable. My friend made distortion measurements on these getting figures below 140dB (at 10kHz - 3rd harmonic).
I also heard that the motor caps made for a customer produced that much harmonics (due to the mechanical structure) that they hardly to the specs - they weren't allowed to produce HF.
I tried several coupling caps in a tube amp and hybrid amp (tube-fet)
Tried 0.47uF styro, combination caps of paper/plastic, MKS, MKP, MKC and 1960's PIO (round) I prefer the latter of all. The best plastic was MKC, but the treble was some harsh, deep bass though. Best soundstage: pio.
For anyone not already aware, a metal bodied oil cap shouldn't normally have its case grounded in a coupling position. A measurement this morning of the capacitance between either lead and the case of an ASC X386S 100uF came in at ~350 pf. The majority of tube circuits won't appreciate being shunted to ground with that much extra capacitance.
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