How Critical Are Coupling Cap Values?

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Woodsage

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How Critical Are Coupling Cap Values?
« on: 28 Sep 2020, 01:56 am »
Hello All,

I think this is probably the best place to ask this question....

How critical are bypass cap values?

I have an integrated tube amp with two, cheap .33 uF 630 volt bypass caps.

I have in stock some very nice AN .22 uF 630 volt caps I would like to try. Good idea or bad idea?  :scratch:

Thanks in advance for any insight.

Mike
« Last Edit: 30 Sep 2020, 11:06 pm by Woodsage »

Speedskater

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Re: How Critical Are Bypass Cap Values?
« Reply #1 on: 29 Sep 2020, 01:13 pm »
The words 'bypass capacitors' have different meanings in different contexts. How are they used?

Woodsage

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Re: How Critical Are Bypass Cap Values?
« Reply #2 on: 29 Sep 2020, 01:59 pm »
Thanks for your reply Speedskater.

These appear to bypass a resistor on the two 6SN7 driver tubes.

Mike

SET Man

Re: How Critical Are Bypass Cap Values?
« Reply #3 on: 29 Sep 2020, 05:31 pm »
Hello All,

I think this is probably the best place to ask this question....

How critical are bypass cap values?

I have an integrated tube amp with two, cheap .33 uF 630 volt bypass caps.

I have in stock some very nice AN .22 uF 630 volt caps I would like to try. Good idea or bad idea?  :scratch:

Thanks in advance for any insight.

Mike

Hey!

   Coupling and bypass are two different things. Bypass is when you piggyback a smaller value cap like .1uf of better quality to usually larger cap to get a better performance. Coupling is the cap connecting one stage to the next stage, like driver tube to output tube or between each section of tube with dual section like the 6SN7.

    From the sound of it and the .33uf value you've mentioned, this sounds more like a coupling cap. If is a coupling cap between the 6SN7 driver stage to output power tube than changing this will have great impact on the sound.

    I have never use the Audio Note caps. But I do have and love the Jensen copper PIO in my SET amps, even compared to some newer caps I've tried. I know Jensen used to make caps for AN, but now they have their own design caps of which are very different.

   Anyway, I'm not an electrical engineer, so I would stick with the same value like the one in your amps right now.

Buddy

Woodsage

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Re: How Critical Are Bypass Cap Values?
« Reply #4 on: 29 Sep 2020, 06:08 pm »
Hi Buddy,

Thanks for your reply.

You’re right, they are coupling caps not bypass caps, I misspoke.

I have used these AN copper in oil caps as coupling caps in the past with very good results.

I’ll pony up and stick with the original .33 value.

Mike

SET Man

Re: How Critical Are Bypass Cap Values?
« Reply #5 on: 29 Sep 2020, 06:39 pm »
Hi Buddy,

Thanks for your reply.

You’re right, they are coupling caps not bypass caps, I misspoke.

I have used these AN copper in oil caps as coupling caps in the past with very good results.

I’ll pony up and stick with the original .33 value.

Mike

Hey!

  Mike, if your AN caps that you've used in the past were made by Jensen then they are different than the current AN caps.

   Anyway, I did changed coupling caps in my SET amps recently, due to one of the Jensen copper PIO cap failed after 20 years. You might be interested in this, you might have to skip through a few unrelated posts there though, but there are some interesting feedbacks from other members here on different caps also.

https://www.audiocircle.com/index.php?topic=166472.0

   By the way, what amp do have there?

Buddy

Woodsage

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Re: How Critical Are Bypass Cap Values?
« Reply #6 on: 29 Sep 2020, 08:07 pm »
Hi Buddy,

I bought these some years back (around 2012 I think) and used them in a Melody EL34 integrated I had back then. They  made a very noticeable improvement and I pulled them when I sold the amp.

Not sure who made them back then but they look identical to the one's I see on Parts Connexion's website. They seem less expensive now than what I paid back then on sale, I hope the new ones sound as good.

I plan on putting them in a Willsenton R8 that is running EL34's.

Mike


Speedskater

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Re: How Critical Are Bypass Cap Values?
« Reply #7 on: 30 Sep 2020, 12:24 pm »
If the cap is in parallel with a resistor, it's not a coupling nor a bypass capacitor. It has some more important task and it's value is important.

Tyson

Re: How Critical Are Bypass Cap Values?
« Reply #8 on: 30 Sep 2020, 05:07 pm »
Hello All,

I think this is probably the best place to ask this question....

How critical are bypass cap values?

I have an integrated tube amp with two, cheap .33 uF 630 volt bypass caps.

I have in stock some very nice AN .22 uF 630 volt caps I would like to try. Good idea or bad idea?  :scratch:

Thanks in advance for any insight.

Mike

Use the same value.  If it's a coupling cap, you don't want to go with a smaller value because it will not pass the full signal (ie, some of the bass gets removed). 

And if it's not a coupling cap, then you really really really don't want to change the value.

Bill Baker

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Re: How Critical Are Bypass Cap Values?
« Reply #9 on: 30 Sep 2020, 08:23 pm »
If it is a coupling capacitor, you may or may not hear a difference due to the difference in value. It all depends on the circuit. As mentioned, you dont want to go too low as the sound could become thin and lacking lower frequencies. To large and the upper ends becomes the victim. Do you have a schematic of the amp?
A bypass cap is usually found on the cathodes of tubes running parallel with a resistor. They are also much lower voltages and usually much higher values. I have never seen a bypass cap that low. There are also some who use bypass caps on power supply caps. While value is not critical here, there are some formulas that some like to go by. PS power supply caps are almost always film caps.

Woodsage

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Re: How Critical Are Coupling Cap Values?
« Reply #10 on: 30 Sep 2020, 11:12 pm »
Thank you Speedskater and Bill Baker.

Yes, they are coupling caps not bypass caps, I got my terminology wrong. I have edited the title to avoid redundancy.

I have read a bit about the sonic changes different values make as you mentioned Bill. I like the way the amp sounds so I’ll order the correct values.

The existing caps are pretty laughable so a worthwhile upgrade I think.

Mike

straitwire

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Re: How Critical Are Coupling Cap Values?
« Reply #11 on: 1 Oct 2020, 12:09 pm »
Improving the quality of your coupling caps can make big difference in the sound of an amp.
You should use the same value if you aren't trying to change the frequency response, and pay attention to the voltage rating also.
You don't want to use a cap that has a much lower voltage rating than the ones you are replacing unless you have measured the voltage and you know it is lower than the caps you are installing.

Speedskater

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Re: How Critical Are Coupling Cap Values?
« Reply #12 on: 1 Oct 2020, 05:16 pm »
With capacitors, there is little correlation between price and suitability.
The most suitable capacitor is seldom the most expensive one.
Stick with the major industrial capacitor manufactures.

avahifi

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Re: How Critical Are Coupling Cap Values?
« Reply #13 on: 1 Oct 2020, 05:31 pm »
Most important rules in replacing capacitors:

1.  Acquire and learn how to use a capacitor meter.  The value of a capacitor is not the number printed on its case, it is the actual measured value.  This value can be substantially different from the printed on the case value depending upon the type of capacitor.

2.  Replace capacitors with measured matched pairs, left to right channel.

3.  Make certain that you are using non-polarized capacitors in any application that specifies this.  Polarized capacitors will break down if reverse voltage is applied to them. In general, most electrolytic capacitors are polarized, most film capacitors are not, but check to make sure unless you want loud BANGS and smoke at turn on.

Frank


rollo

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Re: How Critical Are Coupling Cap Values?
« Reply #14 on: 1 Oct 2020, 06:56 pm »
Most important rules in replacing capacitors:

1.  Acquire and learn how to use a capacitor meter.  The value of a capacitor is not the number printed on its case, it is the actual measured value.  This value can be substantially different from the printed on the case value depending upon the type of capacitor.

2.  Replace capacitors with measured matched pairs, left to right channel.

3.  Make certain that you are using non-polarized capacitors in any application that specifies this.  Polarized capacitors will break down if reverse voltage is applied to them. In general, most electrolytic capacitors are polarized, most film capacitors are not, but check to make sure unless you want loud BANGS and smoke at turn on.

Frank


    Thank you Sir. Good to know.

charles

Woodsage

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Re: How Critical Are Coupling Cap Values?
« Reply #15 on: 2 Oct 2020, 03:28 am »
Thank you everyone for your insights.

And I apologize for the hitch in the giddy up because of my incorrect terminology. I knew they were coupling caps but, being a dotard, I misspoke. Can we still say dotard or is there a new, kinder, gentler way to describe my multitude of infirmities?

Digging a little further into my treasure trove of bits and bobs I found two more of these nice AN Copper Foil Mylar in Oil coupling caps with silver lead outs. Due their age I believe they were made for AN by Tobias Jensen.

Low and behold! they are .1 uF so run in parallel with the .22’s should give me .32 uF which is close enough to .33 uF for these not so golden ears.

Mike