Proper orientation of coupling caps

[pine]

I have been reading a few articles stating that there is a right and wrong way to orient the coupling caps in the amp. They say that the outer foil, sometimes marked with a black line on the old blue Mallory caps, should be the side that faces the grid of the next tube. In my Bandmaster Reverb head, I found that the black line on the cap was facing the tubes. Wouldn't that be facing the plate rather than the grid? I reversed them (for what it's worth I didn't notice much difference). Is the black line now facing the grid, as the article recommends? Have any of you guys noticed a difference when you have the caps one way or another?

[Gtr_tech]

It won't make much difference either way. The "outside foil" (if identified) just serves as a shield if its connected to a part of the circuit at or close to ground. In a coupling application, the grid of the next stage is normally close to 0v, so the outside foil can be connected to that part of the circuit.

[pine]

So am I hooked up with outer foil to grid if the black line faces the tone controls?

[slidincharlie (Carlo P)]

Some techs consider this "black line" or "outside foil" issue like crap, while some others (Gerald Weber among them iirc) say it's an important issue.
I ask to the latter category: how do we orient caps that come without a black line, like orange drops or modern M150 Mallorys?

[dai h.]

if you look a typical tube stage, say a 5F6-A, the correct orientation for the outside foil would be to connect it to the plate. I think lots of people get confused with this but that side is closer to *AC* ground since the plate resistor and the plate resistance of the triode are in parallel with ea. other and the B+ side is at AC ground due to the filter cap being there. Personally, I don't think it does very much and IMO one of those things you might do after doing the things that have more of an effect on the sound worked out and squared away, then wanting to eke that last 0.3% of mice nuts from the amp.

[martin manning]

Some words and explanation here:

http://www.aikenamps.com/OutsideFoil.htm

MPM

[slidincharlie (Carlo P)]

Thank you Martin.
The Aiken pages are so full of info! If I only thought of them any time I need technical help or have a technical dilemma...

[Robert M. Martinelli]

the next step - Shielded caps!

Well, just to split hair in half, why not shield capacitors with copper foil and then tie the foil to GND?

( Maybe I' m only joking - maybe not )

If I think about the good' old days, I still see beautiful handwired amps with their 10% ( carbon ) resistors and 20% capacitors - maybe they were humming a bit, the sound and frequency response could vary from one unit to another due to large tolerances, but still all of them had that certain "something" that makes us love 'em still today...I think a humming '59 Bassman, or an AC30, or - you name it - they all had some imperfections that are part of their mystique.....I' ve also seen some of them with capacitors having the "outer band" connected to the "wrong" side but the amp was sounding good just as well, so, is there actually a point?

This makes me think about a scene from "the naked bullet" series, with Leslie Nielsen and Priscilla Beaulieu/Presley having "safe" sex - some of you surely have seen it - for sure it was safe, but what about the "taste" ?

Aren't we taking away some of the original "flavor" by making things too "perfect" and "aseptic"?

Sorry, just getting nostalgic

Regards

Bob

[dai h.]

yeah but how do you know a "magic" Fender or whatever did not have the caps the "right way" around?

also, "perfect" is a relative thing. For example on a blackface fender it might sound more "correct" with adjustments for low hum, but maybe a noisy hummy Marshall sounds "correct" for someone playing noisy "aggressive" punk rock.

also, since *IMO* orientating the caps don't really do that much anyway, you can't do that much harm, so why not? I think it's attractive since it's easy to do. I mean you have a very high 50/50 chance of getting it correct, right? Pretty good odds.

I would agree with you on the copper foil if you are thinking that an actual (electrostatic) shield would be significantly more effective.

[Enzo]

This is such a silly thing.

People like to state that the outer foil acts as a shield. OK, when connecting the plate of one tube to the grid of the next, exactly WHAT is this shield shielding and from WHAT?

In RF circuits, where a suppressor grid might eb bypassed to ground with a cap, we might then prefer the outer foil to be grounded as a shield. But in audio circuits, the cap acts as a wire as much as anything. Look at some Fender. A wire trails from the tube socket for some plate, travels a couple inches to the eyelet board where the cap sits, then a wire from the other end feeds out a few inches to the treble control on the panel. Now is someone going to tell me with a straight face that the half inch in all that where the cap sits is going to make a difference which way the cap is oriented? ANything in there that we might be shielding the innards of the cap from are going to interact just as easily with all those wires and other component leads.

If you are worried the cap is going to pick up something from nearby circuits, if you orient the outer foil to the following grid, then that foil will pick up the spurious signal. If you orient it the other way, the outer foil will still pick up the unwanted signal which will them pass undaunted through the cap to that grid. What is the difference?

[Robert M. Martinelli]

Hi,
As usual, Enzo's wise words got straight to the point.
When I talked about shielding the caps by covering them with a copper foil tied to GND It was a sort of "provocation".....but then I tried to ring a bell ( "maybe I' m joking, maybe not" ), and also raised some "philosophic" questions.....

As Enzo pointed out, the outer foil is not at GND potential ( except when the application requires it to be that way ).

I completely agree with what Enzo said, to me this matter is much like a guitar cord, we like to think a guitar cord it' s a shielded transmission line, but it actually is an unbalanced one, so the shield actually is part of the transmission line and not a "shield"....If it actually was a "true" shield, it would have been supposed to be tied only on one side to avoid ground loops - To prove it' s not, and that it is indeed part of the transmission line, just try to "play yer guitar" ( thanks Frank! ) using a cord with the "shield" open...

Maybe in one of my next sleepless nights, instead of going around barking at the full moon high in the sky, I' ll grasp my soldering iron in frenzy and I' ll try to shield all my amps' capacitors with copper foil and come back with the results....if any...

Regards

Bob