What coupling capacitor values are common

ryuji · 13th June 2011, 01:02 PM

I'm considering buying a lot of ptfe capacitors for fooling around with amps and circuits. Can get them in large bulk for around 10 cents each between 0.015 and 0.47 uF. Is there a point to having such a variety just for the sake of perfectly duplicating circuits or is it best to work out a favorite value and stick to it. can also get 6.8 uF for when I want the cap to be ' transparent'?

Any other value ranges to look into?

DF96 · 13th June 2011, 02:35 PM

It all depends on what resistance follows, and where you want to put the LF roll-off (open-loop) or LF poles (closed-loop). The idea of 'favourite value' is meaningless. How long is a piece of string? Values I have seen go from 2nF (old radio which didn't do bass!) to 0.68uF. If you want to buy some for playing with then 10nF, 22, 47, 100, 220nF would be a good place to start because you would be within 50% of most reasonable values.

6.8uF would not necessarily be 'transparent'. It would be big, and might increase hum pickup or RF interference. It could even lead to HF instability, simply because of its physical size. Bigger is not necessarily better!

ryuji · 13th June 2011, 02:45 PM

That short list is actually somewhat what I already had in mind, I was thinking the 0.01-0.33 uF range and the 0.1 to 0.47 uF range. Was mostly curious about the 1 to 6 uF range as my current preamp circuit I use has 3.3 uf cap coupling it to the driver tube, I assumed the large value was so that one could adjust cutoff etc based on the dual triodes and the interstage didn't affect anything

DF96 · 13th June 2011, 02:51 PM

You might need 3.3uF if you have a very low grid leak, or you want to listen to earthquakes (and have speakers and ears which go down that far!).

ryuji · 13th June 2011, 02:53 PM

Ah so overall its silly large

DF96 · 13th June 2011, 03:00 PM

As a coupling capacitor for a valve circuit it seems rather large, yes. If the following grid leak is 100K then your LF rolloff is at 0.5Hz.

Apex Jr · 13th June 2011, 03:09 PM

Teflon/PTFE caps at .10 is a bargin....

I'm always asked for .01, .022, .047, and .1Uf
customers still play around and when I'm out of stock I
sell .03 and .068. However I do not have any Teflon caps in stock

What voltage are these caps?

Steve @ Apex Jr

AndrewT · 13th June 2011, 03:15 PM

E6 range from 10pF to 1000pF in both NP0 ceramic and silvered mica.
E6 range from 100pF to 10nF in metallised polypropylene film.
E6 range from 1nF to 470nF in metallised polyester film.

ryuji · 13th June 2011, 03:37 PM

Im sorry, there not ptfe, they are polymer caps, doesnt affect the context of this discussion however. I must have remembered looking at the teflon value range when I wrote about it

TG · 13th June 2011, 07:03 PM

I bought 50 pcs of 0.33uF caps several years ago for coupling job in tube amps, and I'm quite happy with that value, never really needed something else. Last month bought another 30 pcs of the same value, and I hope to be happy again for some time.
In general I'd say that 0.22 or 0.33 or 0.47uF is a pretty universal choice.

13th June 2011, 01:02 PM	#1
ryuji diyAudio Member Join Date: Feb 2011 Location: massachusetts	What coupling capacitor values are common I'm considering buying a lot of ptfe capacitors for fooling around with amps and circuits. Can get them in large bulk for around 10 cents each between 0.015 and 0.47 uF. Is there a point to having such a variety just for the sake of perfectly duplicating circuits or is it best to work out a favorite value and stick to it. can also get 6.8 uF for when I want the cap to be ' transparent'? Any other value ranges to look into?

13th June 2011, 03:15 PM	#8
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	E6 range from 10pF to 1000pF in both NP0 ceramic and silvered mica. E6 range from 100pF to 10nF in metallised polypropylene film. E6 range from 1nF to 470nF in metallised polyester film. __________________ regards Andrew T.

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13th June 2011, 02:35 PM	#2
DF96 diyAudio Member Join Date: May 2007	It all depends on what resistance follows, and where you want to put the LF roll-off (open-loop) or LF poles (closed-loop). The idea of 'favourite value' is meaningless. How long is a piece of string? Values I have seen go from 2nF (old radio which didn't do bass!) to 0.68uF. If you want to buy some for playing with then 10nF, 22, 47, 100, 220nF would be a good place to start because you would be within 50% of most reasonable values. 6.8uF would not necessarily be 'transparent'. It would be big, and might increase hum pickup or RF interference. It could even lead to HF instability, simply because of its physical size. Bigger is not necessarily better!

13th June 2011, 02:45 PM	#3
ryuji diyAudio Member Join Date: Feb 2011 Location: massachusetts	That short list is actually somewhat what I already had in mind, I was thinking the 0.01-0.33 uF range and the 0.1 to 0.47 uF range. Was mostly curious about the 1 to 6 uF range as my current preamp circuit I use has 3.3 uf cap coupling it to the driver tube, I assumed the large value was so that one could adjust cutoff etc based on the dual triodes and the interstage didn't affect anything

13th June 2011, 02:51 PM	#4
DF96 diyAudio Member Join Date: May 2007	You might need 3.3uF if you have a very low grid leak, or you want to listen to earthquakes (and have speakers and ears which go down that far!).

13th June 2011, 02:53 PM	#5
ryuji diyAudio Member Join Date: Feb 2011 Location: massachusetts	Ah so overall its silly large

13th June 2011, 03:00 PM	#6
DF96 diyAudio Member Join Date: May 2007	As a coupling capacitor for a valve circuit it seems rather large, yes. If the following grid leak is 100K then your LF rolloff is at 0.5Hz.

13th June 2011, 03:09 PM	#7
Apex Jr diyAudio Member Join Date: Jun 2002 Location: Torrance, Calif	Teflon/PTFE caps at .10 is a bargin.... I'm always asked for .01, .022, .047, and .1Uf customers still play around and when I'm out of stock I sell .03 and .068. However I do not have any Teflon caps in stock What voltage are these caps? Steve @ Apex Jr

13th June 2011, 03:37 PM	#9
ryuji diyAudio Member Join Date: Feb 2011 Location: massachusetts	Im sorry, there not ptfe, they are polymer caps, doesnt affect the context of this discussion however. I must have remembered looking at the teflon value range when I wrote about it

13th June 2011, 07:03 PM	#10
TG diyAudio Member Join Date: May 2002 Location: Kiev, Ukraine	I bought 50 pcs of 0.33uF caps several years ago for coupling job in tube amps, and I'm quite happy with that value, never really needed something else. Last month bought another 30 pcs of the same value, and I hope to be happy again for some time. In general I'd say that 0.22 or 0.33 or 0.47uF is a pretty universal choice.

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