ground side for mallory 150's

[scole]

is it true that when reading the printing on the cap from left to right, you ground the right side? or that side goes to the tube pins?. this is from vacuum tube valley........

Capacitor Installation Tips: Remember to connect the inner foil side facing the output. In coupling caps, this means connecting the inner foil to the grid of the output tube and the outer foil to the plate of the driver tube. On some caps, the color of the wire indicates the inner foil side, on some the inner foil is marked and on others it is typically the right side of the cap when reading the value. On older caps, the outer foil is indicated by a band around the cap.

[dai h.]

go to the amp garage(dumble/trainwreck) site and look up the discussions on where to place the outer foil. And also check out the Aiken site for the article there as well. I don't really think it does much but shouldn't hurt anything to try.

[scole]

aiken says use a scope to find the inner foil. im wondering if there is a way you can do it if you dont have a scope?

[stokes]

You can roll a piece of foil around the body of the cap and then read the capacitance from one lead to the foil and then from the other lead to the foil.I believe the lead that reads the higher capacitance is the outer.You will need a cap meter that will read very small amounts of capacitance.

[dai h.]

not sure I'm misremembering but wasn't there something about using a finger to induce noise in one or more of the threads?

[scole]

yes dai, this is from aikens page.

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.

[dai h.]

you know the solution to this sort of noise problem is to never ever squeeze the cap tightly with your fingers especially while you are playing your amp.

[bob p]

you know the solution to this sort of noise problem is to never ever squeeze the cap tightly with your fingers especially while you are playing your amp.

[Enzo]

I hope you are not grounding EITHER end of your coupling caps. There is no shielding to be done at audio freqs in our amps. As far as the audio signal is concerned, both sides of a cap are just parts of the same conductor. In a cap connecting a plate to a following grid, WHAT would be shielded from WHAT by this cap ? Any radiated signal the cap might pick up would be equally picked up at either end.

[Chuck H]

Enzo

I think the intention with the "shield" notion is that in certain cap designs one lead will be connected to the outermost foil. With that in mind you should connect that lead to the end of the circuit that is nearest to ground and therefore gain "some" shielding. There are circumstances other than decoupling where this might prove more effective. I personally never thought that there would be enough advantage to bother with it. But I don't have the facts to poo poo it either.

Some say they CAN hear a difference and that the outer foil lead should be connected to the plate end of the circuit for decoupling. Marshall did this on some models with a shielded cable on the input grid lead with the shield connected to the plate of that triode. Others have done this too. Wether it was a matter of shielding from a different source or trying to pick up more plate to grid capacitance I don't know.

Chuck

[dai h.]

the shield connected to the plate is a "cap"(capacitance) from output to input to help suppress oscillation. IIRC someone mentioned Soldano did not bother with doing the "correct polarity" thing. *Assuming* this is true, and looking at all the other things they did(grounding, layout differences to keep noise low, increase stability for ex. moving the preamp tubes close to the front panel which reduces all the lengths of the wires to the preamp tubes which means less of the signal is exposed and at the same time less area to radiate signal, filaments laid in such a way to have them ideal--close to chassis for good cap coupling, 90 degree angle to other socket wires, other things they probably did with parts positioning, etc., etc.), that is if they obviously DID all that (SLO100 being a high gain and very potentially a noisy mess if done wrong) but DID'NT bother to put the caps in the correct orientation, then how much of a practical effect does that have really?--it makes one wonder. This difference that some "swear", is this swearing that they could hear a difference using the method specifically meant to tell (inducing hum from your body)--which is not normal operation? Or, some sort of improvement in noise or tone? I suspect orienting "correctly" is more of an insignificant or extremely subtle effect and that physical orientation of the cap probably has much more(i.e. very obvious hum if not correct) effect. I don't want to stop anyone from experimenting and if you wan't to try it you should do it but I never noticed anything from flipping them.

[Tobacco Soup]

It helps reduce RF interference. I do it on coupling caps only, but for me it is easy because the outer foil ends have been marked by the factory (i.e.old & NOS C-Dubs). To me, this is a hobby and doing this just adds to the 'fun'. In fact, this is good fun because it's the hands-on part. If I were in it for profit, I would experiment first, but I doubt it would be a mfg. procedure.

There are a million factors involved, but my Plexi build using these caps and orienting the outer foil to an AC ground made this amp dead quiet. Like, after a little surge/pop, you could hear the transformer buzzing but not the amp through the speakers until you played (on a clean setting). YMMV.

[Enzo]

I guess one has to come up with a rationale, outer foil shielding inner? That means the outer foil is the one connected to the following grid. That wouldn't shield it from RF. That would expose more of it. When I look at a plate coupling to a grid, niether one is AC ground, and in fact neither is DC ground. Just one has the lower DC voltage sitting there. AC ground would kill your signal, and DC ground your well DC. That grid still sits 470k or whatever from ground.

I don't think too much about RF after the input stage as a rule.

I am still not persuaded that both ends of the cap are not equally sensitive to the freqs passing through the following stage.

[Chuck H]

Enzo,

If you read my post above, you know that I'm not convinced either. But where I am not inclined to trouble with the truth until my next build (and then only if time allows), I know you are notorious for saying 'well just do it and find out'. So even though the logic says "outer foil, shmouter foil", we can't REALLY poo poo it until we give it an honest try. After all, some people have already stated that they have noticed a difference.

I think I'm defending the possibility because I'm one of those guys that believes he can hear a difference in some film caps and I have been poo poo'ed for it. And even though all manner of theory and math was thrown my way, it seemed to me that only the parts supporting my opposition were noted. So, not being tech enough to fight back, I had to simply say "I adamantly reject your reality and substitute my own."

Chuck

[dai h.]

That means the outer foil is the one connected to the following grid. That wouldn't shield it from RF. That would expose more of it. When I look at a plate coupling to a grid, niether one is AC ground, and in fact neither is DC ground.

the rationale (as I understand it) is to put the outer foil on the side closer to ground. So for examp. on a typical amp, say 5F6-A/Marshall 1st stage, the outer foil connects towards the plate, since (from an AC perspective) the plate R and plate resistance are in parallel, and these are connected (via the local 8uF filter) to AC ground. The other side is connected to DC ground through the 1Meg pot. Therefore, the plate side is closer to (AC) ground. What I've read from a couple of sources is that with high freqs.(RF) "correct" orientation provides a bit of a shielding effect. (Perhaps a case of magnifying a small truth into something it isn't?) "Correct" orientation is also said to attract less dust which might be important for equipment left running for very long periods.