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On Capacitors..

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Posted on April 24, 2016 at 07:45:43
Lee of Omaha
Dealer

Posts: 1800
Location: Omaha NE
Joined: September 8, 2006
OK, I'm a late convert to the importance of capacitors. We recently modified a Dynaco ST-70 with our standard mod except the customer opted for Russian K-40Y paper in oil coupling caps, instead of the standard good quality film caps. The difference was startling. With the K-40Ys the amp dropped all character-it just seems to pass music.

I've read about how caps depart from ideal. There's resistance, inductance, and they can be modeled as a capacitor in parallel with a number of RCs. While I've never seen a good explanation of this phenomenon, I suspect it has to do with a little leakage into and out of the dielectric, and with electrostatically wrenching electrons inside the dielectric around a little (which would lead to both the little capacitances and the little resistances as the electrons are moved and then resistively relax back into place). Some inductance is unavoidable in the leads.

That leads me to the question. Has anyone tried expensive, volumetrically inefficient vacuum capacitors? They should have no dielectric-related misbehavior. Maybe good for RIAA equalization? Or coupling caps if you like room-sized amps? It also occurred to me that due to their size and shape they might be microphonic.

 

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RE: On Capacitors.., posted on April 24, 2016 at 08:40:31
Alpha Al
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Posts: 2957
Location: N. Carolina
Joined: February 16, 2004
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December 3, 2015
Vacuum capacitors are used for RF applications where there is a lot of voltage present.

They are large in size, and usually small in capacitance, down in the pF range.

 

RE: On Capacitors.., posted on April 24, 2016 at 16:02:09
Paul Joppa
Industry Professional

Posts: 7294
Location: Seattle, WA
Joined: April 23, 2001
Air dielectric variable caps do exist; they were used for many decades in radio tuners. Air is nearly as linear as vacuum ...

I believe they have been used in RIAA circuits at fairly high impedances - I get 2.13Meg + 310K resistances with 1000pF + 343pF caps. If you have the gear, you can trim then exactly. Most often the capacitance is in the range 250pF to 500pF but they usually have at least two caps on the same shaft, which can be paralleled. Be aware that grid leakage in the next stage could easily throw things off.

 

RE: On Capacitors.., posted on April 24, 2016 at 18:06:23
Jim McShane
Dealer

Posts: 5910
Location: Chicago
Joined: January 13, 2003
Lee, your experience runs counter to (I'd say) 95% plus of the experiences I've had personally or have knowledge of.

I can tell you that often the older caps (especially older Mylar/polyester caps) have a bit of "snap" to them and for a while the K40s can sound a bit dull until you get accustomed to them not having that "snap".

I recommend to people that in vintage gear especially they use a mix of film and K40 caps - that's hard to do in a ST-70 since the output couplers are the only coupling caps.

But don't condemn the K40s based on the one experience. They can make outstanding tone when used properly and with the right associated components/parts.

I'm no help on the vacuum caps though, sorry.

Edited to fix typo...

 

RE: On Capacitors.., posted on April 24, 2016 at 18:11:42
Lee of Omaha
Dealer

Posts: 1800
Location: Omaha NE
Joined: September 8, 2006
Jim,

I wasn't damning the K40Ys, I was praising them! With the paper in oils, the amp had no character (maybe "color" would have been a clearer term). In other words, it didn't seem to add or detract from the music passing through it. I can think of no higher praise.

 

RE: On Capacitors.., posted on April 25, 2016 at 01:03:21
Michael Samra
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Posts: 36118
Location: saginaw michigan
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The K40y caps are absolutely incredible.So many were reluctant to try then and then when they do,almost everyone is floored by them...I knew what you meant when you said they pass music because they are so linear with frequency change. I think some of it has to do with the oil reducing friction inside the cap.Also,the paper caps are very stable at higher frequencies.Glad you like them.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: On Capacitors.., posted on April 25, 2016 at 08:21:36
Jim McShane
Dealer

Posts: 5910
Location: Chicago
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Lee, my apologies - I interpreted your post to mean you were disappointed! Thanks for setting me straight.

 

RE: My eye opening experience with K40s...., posted on April 25, 2016 at 09:47:47
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
occurred when i installed all new caps in a Marantz 7 preamp, (it is what the owner wanted). After that was finished and i fired up the preamp for the first time I thought, oh,oh, this did not turn out good. The sound was dull and seemed compressed and frequency limited. But after about 30 hours you could hear the music start to come through with much better clarity and focus. And after about 50 hours it sounded really really good . It seemed to me that the caps required a definite break in period. My only gripe is they made the leads on those caps too short. cheers, Dak

 

RE: On Capacitors.., posted on April 25, 2016 at 12:52:57
dhsettim
Audiophile

Posts: 181
Joined: January 10, 2002
On Ebay I have seen, more recently, some KBG oil capacitors.
0.1uF 600V PIO Capacitor KBG-M2.
They seem to be similar but more expensive than K40Ys.
Anyone have experience of them?
best
tim

 

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