After identifying the outside foil side of a coupling capacitor, how do I determine the correct orientation to solder it to a PCB in my Class A parallel tube amp?
Obviously I’m pretty green to electronics and if someone would be kind enough to explain it in layman’s terms or can see the side in the photos it would be much appreciated.
Thanks
Obviously I’m pretty green to electronics and if someone would be kind enough to explain it in layman’s terms or can see the side in the photos it would be much appreciated.
Thanks
Attachments
The outer foil should be connected to the lower impedance of the two connection points.
That's determined by looking at the schematic and understanding how the circuit works.
If you post your schematic, the best connection option could be suggested.
That's determined by looking at the schematic and understanding how the circuit works.
If you post your schematic, the best connection option could be suggested.
I see what the difficulty maybe here. Lots of people watching MrCarlson channel...
I am still not sure it matters. We are not trying to calibrate SW radio receivers here.
In any case, you will need to distinguish the caps to ground vs the coupling caps. All the caps to gnd the outerfoil goes to gnd, obviously. For the interstage, the direction of the signal is important, the exit of one stage should be the outerfoil and the grid of the following stage should be the inner terminal of the cap. The idea is to shield the grid, gate of base of the next device downstream of your signal. I cannot think of any other case where you have a high impedance feeding a low impedance but hey, I have been wrong before. 😉
I am still not sure it matters. We are not trying to calibrate SW radio receivers here.
In any case, you will need to distinguish the caps to ground vs the coupling caps. All the caps to gnd the outerfoil goes to gnd, obviously. For the interstage, the direction of the signal is important, the exit of one stage should be the outerfoil and the grid of the following stage should be the inner terminal of the cap. The idea is to shield the grid, gate of base of the next device downstream of your signal. I cannot think of any other case where you have a high impedance feeding a low impedance but hey, I have been wrong before. 😉
Should be easy enough to find the correct end for the foil of a coupling capacitor using a voltmeter. If it's the input to a cathode follower then the foil should go to the end that doesn't have any DC on it. For everything else, foil should go to the terminal that does have DC on it.
"Should be easy enough to find the correct end for the foil of a coupling capacitor using a voltmeter. If it's the input to a cathode follower then the foil should go to the end that doesn't have any DC on it. For everything else, foil should go to the terminal that does have DC on it.”
That’s what I needed. Thanks
Like I said I’m a noob. 👍
That’s what I needed. Thanks
Like I said I’m a noob. 👍
For the drive schematic, both C1 and C4 should have their outer foil as the left terminal (or input).
https://www.aikenamps.com/index.php/where-to-connect-the-outside-foil-on-capacitors#:~:text=Since the capacitor is wound,indicate the outer foil position.
" If the capacitor has no banded end, the outside foil connection could be on either end, so there is no easy visual method to determine the best orientation of the capacitor. However, if you have access to an oscilloscope, you can do a simple test to determine which is the outside foil terminal. Set the scope up to the most sensitive vertical scale (20mV or less, preferably) and connect the scope probe across the capacitor (ground to one side of the cap, probe tip to the other). Grab the capacitor tightly with your fingers, and note the amplitude of the induced 60Hz AC signal (or 50Hz if you are on the other side of the pond). While still holding the capacitor tightly, reverse the scope leads and you should see a dramatic difference in the amplitude of the induced AC signal. The orientation with the lowest induced signal is the one you want, and the ground lead of the scope is connected to the outside foil in that position. Mark it, and connect that side of the cap to the lowest impedance point in the circuit, typically the driving source plate when used as a coupling cap, or the grounded end if used in a shunt position. If you cannot see a large enough induced AC signal by holding the capacitor between your fingers, place the capacitor on top of an AC line cord (that is plugged into the mains wall socket, of course!) instead of holding it between your fingers and you will see a larger signal on the scope. If you are new at this, start with a 0.022uF cap or thereabouts, as it is easiest to see the difference between the two orientations. The induced signal is smaller at 60Hz with larger value capacitors, and is more difficult to see on the scope."
" If the capacitor has no banded end, the outside foil connection could be on either end, so there is no easy visual method to determine the best orientation of the capacitor. However, if you have access to an oscilloscope, you can do a simple test to determine which is the outside foil terminal. Set the scope up to the most sensitive vertical scale (20mV or less, preferably) and connect the scope probe across the capacitor (ground to one side of the cap, probe tip to the other). Grab the capacitor tightly with your fingers, and note the amplitude of the induced 60Hz AC signal (or 50Hz if you are on the other side of the pond). While still holding the capacitor tightly, reverse the scope leads and you should see a dramatic difference in the amplitude of the induced AC signal. The orientation with the lowest induced signal is the one you want, and the ground lead of the scope is connected to the outside foil in that position. Mark it, and connect that side of the cap to the lowest impedance point in the circuit, typically the driving source plate when used as a coupling cap, or the grounded end if used in a shunt position. If you cannot see a large enough induced AC signal by holding the capacitor between your fingers, place the capacitor on top of an AC line cord (that is plugged into the mains wall socket, of course!) instead of holding it between your fingers and you will see a larger signal on the scope. If you are new at this, start with a 0.022uF cap or thereabouts, as it is easiest to see the difference between the two orientations. The induced signal is smaller at 60Hz with larger value capacitors, and is more difficult to see on the scope."
I did try that and It didn't work for me at all. The amount of random noise variation is equivalent and I could not tell the two ends apart from each other.
I really tried to understand the "good" reason for connecting the outer foil to the lower impedance side of the capacitor.
I don't buy the reasons showed and linked to here. Very close to call it BS.
Shielding purpouses by connecting through the power supplies electrolytical caps that "basically" are grounded??????????
The anode resistor of this amplifier is probably 100k or more.
Grounding through a 100 kOhm resistor is not anywhere near what would be considered as grounding. Maximum impedance for ground is in grid terms less than 25 ohm.
Beside that, output impedance of V1b will be much less than the anode resistor so the lowest impedance route to ground would be through V1b.
Mumblojumblo.
C1 can be shorted by a piece of wire if you are 100% sure that you can guarantee that you have no DC at the input.
Any DC might ruin the woofers of your loudspeakers and decorate your pants with a brown strip. So it's a risk you need to fully understand.
Shorting of C1 will probably give you a little bit clearer sound.
Don't expect anything major, but there is no cap like no cap at all.
I would be more worried about the capacitors C3, C5, C6 and C7 since they are electrolytical caps and have more of a sonic impact than any foil coupling cap.
These need to be of the highest quality possible. Decoupling them with some small size metalized or foil capacitors might help the sound quality.
If I built the amplifier none of these would have been in the signal chain at all. Fixed bias of output tubes is what I would have used.
C2 have a very strange position.
I suspects it's there as a frequency limiter. On a tube that isn't in the global feedback loop and varies with the setting of the potentiometer???
No funcionality in eigther of the ends of potentiometer and maximum funtionality in the middle of the potentiometer.
It would be better placed between V1a anod and ground and probably reduced in size to limit frequency range for V1b that is in the global feedback loop.
Will prevent risk of overshoot and oscillation because of limited high frequency capacity of the output transformer.
If it's there for stability reasons for V1a I would have put in a 1kOhm series resistor to grid of V1a instead. Less sonic impact, and full range functionality.
Also remember that any modification of you amplifier probably will void warranty. Don't mess with it before out of warranty.
I don't buy the reasons showed and linked to here. Very close to call it BS.
Shielding purpouses by connecting through the power supplies electrolytical caps that "basically" are grounded??????????
The anode resistor of this amplifier is probably 100k or more.
Grounding through a 100 kOhm resistor is not anywhere near what would be considered as grounding. Maximum impedance for ground is in grid terms less than 25 ohm.
Beside that, output impedance of V1b will be much less than the anode resistor so the lowest impedance route to ground would be through V1b.
Mumblojumblo.
C1 can be shorted by a piece of wire if you are 100% sure that you can guarantee that you have no DC at the input.
Any DC might ruin the woofers of your loudspeakers and decorate your pants with a brown strip. So it's a risk you need to fully understand.
Shorting of C1 will probably give you a little bit clearer sound.
Don't expect anything major, but there is no cap like no cap at all.
I would be more worried about the capacitors C3, C5, C6 and C7 since they are electrolytical caps and have more of a sonic impact than any foil coupling cap.
These need to be of the highest quality possible. Decoupling them with some small size metalized or foil capacitors might help the sound quality.
If I built the amplifier none of these would have been in the signal chain at all. Fixed bias of output tubes is what I would have used.
C2 have a very strange position.
I suspects it's there as a frequency limiter. On a tube that isn't in the global feedback loop and varies with the setting of the potentiometer???
No funcionality in eigther of the ends of potentiometer and maximum funtionality in the middle of the potentiometer.
It would be better placed between V1a anod and ground and probably reduced in size to limit frequency range for V1b that is in the global feedback loop.
Will prevent risk of overshoot and oscillation because of limited high frequency capacity of the output transformer.
If it's there for stability reasons for V1a I would have put in a 1kOhm series resistor to grid of V1a instead. Less sonic impact, and full range functionality.
Also remember that any modification of you amplifier probably will void warranty. Don't mess with it before out of warranty.
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Seems like someone made a sound decision to select Elna Silmic II capacitors which is one of the better electrolytics out there.
Looks like a modification...
Performed by you MetalMatt?
Looks like a modification...
Performed by you MetalMatt?
Yes flex2, I replaced all the lelon caps with elna silmic 2, audio note Kaisei and Mundorf mlytic caps
Unfortunately I am too new to electronics for this to make sense to me. Can you make it easier to understand for a noob?
Thanks
I am under the impression that on smaller caps, say below 1uF it really doesn't make any difference. The fact that Solen starts to label the outer foil only above a certain value (forgot what that is exactly) kind of bolsters my argument.
Oooh.
Lot's to say about different dielectric materials of capacitors.
All capacitors have ESR specified at different frequencies and is a quantified value of the series resistance of the capacitor.
ESR = Equivalent Series Resistance.
ESR influence at what speed a capacitor can be charged and how fast it can release stored energy.
In general electrolytical capacitors use dielectric materials that have a high ESR which means that they are quite slow to load and release energy.
Some have lower ESR and reacts faster to changes in voltage.
But's it's not all about lowest possible ESR, it's also about the linearity of ESR, and ESR usually increase with higher frequencies.
Dielectrics used in foil and metalized capacitors make them able to have much less ESR which make them much faster to react to changes in voltage potential, and the reason for putting a small fast capacitor in parallell to a electrolytic slower capacitor is to keep the ESR low at higher frequencies since the electrolytic usually have higher ESR at higher frequencies.
It's a matter of keeping the ESR as linear as possible over an broad frequency range.
Silmic II which you use have silk fibers blended in one of the dielectrics which gives it somewhat different ESR properties than other electrolytical capacitors and because of that a little bit different sound.
Our ear is extremely sensitive to harmonics of instruments and how harmonic distortion is added to that mix of harmonics originating from the instruments of the recording. That's why a recording sounds different with different electronics used and capacitors, beside all other parts like resistors, wires, tubes etc, have a sonic impact depending on how linear they are and how they change the harmonics of the recording and how harmonics of distortion is added to the mix.
All capacitors you have changed are "good" choices and it's not sure a smaller foil capacitor in parallell will have a detectable sonic impact.
Sorry...
Tried to make it simple but I feel that I failed.
I'm afraid I would disagree with flex2 on ESR. ESR really is a resistance and it's the resistance of the leads and the capacitor's two plates; the dielectric does not come into it. Also, being a resistance, ESR is constant with frequency. But there's another component in series (not just resistance), and that's the inductance of the leads and the plates (Equivalent Series inductance, usually called ESL). Almost all capacitors are made as foil either side of the dielectric and are then rolled into a cylinder. If the foils are slightly offset, then one end of the rolled assembly is one foil, the other end the other foil. The ends can be sprayed with liquid zinc to make a low inductance (ESL) and resistance (ESR) path to all parts of the plate. You can't do that with an electrolytic capacitor; you have to make a connection to the foil with a tab. Once upon a time, electrolytic capacitors were made very badly with the tab at one end of the foil. Stupid, but I dissected a capacitor made in that way (not recommended as electrolytic capacitors contain acid). That's why it once made sense to bypass electrolytic capacitors with film capacitors. Moving the tab to halfway along the foil greatly reduces inductance. These days, almost all capacitors (including electrolytics) have about 15nH of ESL if measured close to their body. Inductance of a wire is very roughly 3/4nH per mm, so if you measure 10mm away on each lead, you've added 7.5nH per lead, or 15nH, doubling ESL.