2a3 Capacitor question

debk

debk

New member
I know there has been multiple threads on the parafeed capacitor value, and I have read them. I just ordered the paramount , and I just want to make sure I have this correct.
I already have a 300b amp so I am going to build the Paramounts for 2a3 tubes from the get go.

From what I understand the kit comes with a 3.3uf parafeed capacitor.  From what i have read the ideal value for a 2a3 paramount with the standard iron is around 5.6uf to 6.8uf.  With the MQ iron using the Paramour plate choke (BH-6 or BCP-15) the ideal value is around 10uf.

I plan on upgrading to the MQ iron after I have had some time to listen to it with the standard iron.

So since decent capacitors in this size are fairly expensive, would I be ok just building it to start with with the included capacitor, and then upgrading to he 10uf when I upgrade the iron?  Or should I just start with a 10uf capacitor or would you suggest something else entirely? 

Also I have read that you should not use the Mundorf silver/oil in the 2a3 paramount because of the heat produced.  Is this really an issue with the 2a3 version?  Would it alos be an issue with the Silver-gold/oil capacitors?  I have not had much luck finding the operating temperature specs for these mundorfs. 

Thanks for any help

Debra
 
Debra,

I know that there has been mention about a possible issue using the Mundorf silver/oild caps, but have been using them in my amp for over 4 years with no problem.
 
Debra,

The standard capacitor will give you a good response.  In realistic rooms you won't hear a difference in bass response between the 3.3uF and 6.8uF.  If your speakers are flat at 20 Hz or 40 Hz it takes a long room to give you that deep a response.

I bought the BCP-15 and TFA 2004 (Sr) for use in my 2A3 Paramours.  I went with the incredibly cheap 10uF Obbligato black Film in Oil caps.  I haven't upgraded in 5 years.  The 10uF value was needed with the MQ iron I bought to get equivalent response to the stock cap and iron.
 
I'm out of town (in Virginia) for 10 days and don't have all my resources handy. But if you find the Cornell-Dubilier web site they have some extensive information on various capacitors, including the effect of heat on lifespan. Bottom line, there is no such thing as a magic temperature marking the boundary between exploding and living forever... cooler is always better.

For what it's worth the 2A3 direct coupled version dissipates much more heat from the cathode resistors, because the cathode is at 260 volts.

Capacitor value: my estimate for the best value is 2*L/R squared - L being inductance and R the transformer primary impedance. At this value, the impedance presented to the tube drops slightly (2/3 the midrange value? Sorry I don't have my simulations at hand) in the deep bass, then rises as the capacitor dominates at lower frequencies. Note that some Japanese audiophiles use much larger capacitances. Even the largest cap will perform much like a series feed arrangement; one of the parafeed virtues is a more resistive, higher impedance load presented to the tube at the lowest frequencies.

A smaller capacitance raises the cutoff frequency (roughly as the square root of the capacitance), but provides the tube with a safer minimum load. Somewhere around half the nominal capacitance the load never drops below the midrange value. In general I think this is a good compromise for using the 45 because it keeps the distortion low at maximum power. Smaller than that, you lose bass extension without getting any benefit in return.

Conversely, a larger capacitance will deepen the bass extension for small signals, at the price of possible distortion with large low-frequency signals. Since I run 101dB speakers with 300Bs, I use a 6uF cap in my Paramounts - I'm not likely to run out of steam. Around twice the nominal value, the load impedance benefits become small relative to a regular series feed.

Keep in mind that this assumes a perfect power supply, and a speaker impedance that is a pure 8 ohm resistor. There will be some interaction with both impedances, so the generalizations above should be taken with a grain of salt. I recommend experimentation with the target speakers in the target room - listen for bass distortion and extension. Once you know what capacitance works best, then you can spend some bucks on higher quality caps to get cleaner treble. I'd get a ~6uF cap, and parallel the 3.3 to get 10uF - gives you three values to listen to.

Well, not the answer you were hoping for, but food for thought. So much of engineering is not answers so much as the art of compromise...
 
Paul

Thanks for an excellent explanations. It is certainly an answer that makes sense and a great plan of attack for the problem.

I appreciate it

Debra
 
Deb,

Thank you for starting this very helpful thread.  Because of it, I picked up a pair of used Mundorf Silver in Oil 5.6 uF caps to try out.  I've been very happy with the Mundorf SIO caps in my Stereomour. 

Best,
John
 
Thanks John

I oo have used Mundorf in a number of my builds, and have been very impressed.

Please let us know how they sound and hold up.

I am thinking of trying the Clarity Cap MR. I hear they sound very good and have a higher temperature rating


Deb
 
Hey John - Used Mundorf silver/oils sounds like a good way to go. Where did you get them, and how was the condition? I would like to use all silver/oils in my speakers. Now I just have my ampohm's bypassed with small silver/oils. One thing I can say is the addition of the silver/oils really smoothed things out. I also used the silver/oils in the Quickie.
 
Deb,  I'll definitely post my thoughts, such as they are, on the Mundorf SIO caps.  Those Clarity MR caps look good...excellent comments by those who have tried them and a 100 degree C. temperature rating. 

Earwaxxer, I found them on AudioCircle...I think they were used in a speaker crossover.  They are pretty good with reasonable long leads still. They tested at 5.690 and 5.705.  There are still some 15 uF caps left if that helps.  I found they smoothed out my Stereomour very much, too.  I'm a big fan of the SIOs...

Best,
John
 
After having lived with the MR caps in my Quickie and Sex amp I have to warn all of you that they're extremely revealing.  They brought a huge leap in separation and clarity at first.  I have over 300 hours on them now and they really haven't changed much.  They could be a little rough in the first 100 hours but have smoothed out since.  Still, they hold nothing back and cannot be considered warm at all.  Sometimes they remind me of the sound of Krell gear: cool and clean but not as forgiving as I would like. 

I previously used Clarity ESA caps which are much more forgiving and a bit warmer in the upper treble.  The ESA are still very good with detail but lose a lot of depth and ambiance compared to the MR caps.  If the the MR caps rate a 10 in clarity then the ESA come to about a 6-7.  I'm thinking of going back to the ESA just to see if I like them better.  It's hard to give up the extremely clean and clear sound of the MR caps but sometimes they are so revealing they make listening to some of my favorite recordings unbearable.

I may also try the Jupiter and Mundorf caps for a warmer flavor.
 
Hey Rob - Interesting observations with the Clarity MR's. Seems pretty consistent with other reviews. I think thats why I tended to error on the side of the oilers. It would be interesting how an MR would sound bypassed with a small oil like a Mundorf SIO, or GSIO. 

Cheers - Eric
 
That's an interesting idea.
How about a small teflon for the bypass

What value would you use for the bypass capacitor?
I have a pair of 0.22uf Vcap TFTF sitting around.

Debra
 
I have the Mundorf silver/oil caps in my Paramount's, but never thought to add a bypass cap to them. I have a pair of Russian Teflon 0.1uF caps that I could try. I think that I will start burning them in.
 
Hey Brad - Not sure you would gain anything bypassing such a good cap. I think the general consensus is to only bypass when you really cant afford to upgrade the cap in question. Bypassing is a double edged sword. The caps have to play well together. The Mundorf silver/oils IMO have all the desirable characteristics of the best caps (clean, but organic, good soundstage, lack of glare, good separation of instruments, low noise) .  Adding a teflon may sterilize things a bit. Make it a bit too clean. If your system is already a bit too organic and tubie, that could be a good thing. Curious to hear how it works in your system though.
 
So is the consensus that he Mundorf silver/oil is ok with the 2a3 Paramount?

Don't want to spend the money on them is they will have a problem with the heat


Debra
 
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