which end is ground on this mylar bypass cap?

[deci belle]

Will some one please help me figure out which end is (+) or (-)?

I just got a mylar cap for a Marshall jtm45 preamp. It is a .68µF 50v 5% mylar axial cap manufactured by Alec (I think).

A fine blue line wraps around one end of the cap (measures 1/2" x 1" and is clear/silvery/white color).

Anyone familiar with this type of cap?

Thanks very much!

Mar'

[nashvillebill]

Mylars aren't polarized.

[deci belle]

hahahaha!! cool, Bill!! haha! Thanks, man!

[defaced]

That blue line probably indicates the outer foil. It's not polarized per se, but the foil acts as the shield for the cap and you may find the circuit is quieter with the shield one way vs the other - depends on what the cap is doing in the circuit.

[nashvillebill]

I started to mention that, but I've heard conflicting opinions on whether it actually makes a difference at audio frequencies...

[R.G.]

I started to mention that, but I've heard conflicting opinions on whether it actually makes a difference at audio frequencies...

Everything - right down to and including the color of the paint/covering - has been used to advertise some mojo-vintage-brown-clarity-tone goodness for caps. And every other component.

[deci belle]

I put it in with my eyes closed to tease the mojo-gods!! It was a blue line…

[trem]

Everything - right down to and including the color of the paint/covering - has been used to advertise some mojo-vintage-brown-clarity-tone goodness for caps. And every other component.

I will not even ask you about the capacitor "Break-In" / "Burn-In" that Sozo claims improves their caps.....
Anyway, I have seen a few Youtube demos that address "outer foil" noise of caps. It sure does seem to show up on a scope, or when amplified when I see these things on the Internet. But I have never been able to hear the difference. It my make more of a difference in some positions than in others, and different caps may be more susceptible by design or tolerance....I do not know. How do you approach the issue of cap outer foil.? Which side goes where.?
Thank You

[Enzo]

I saw it so many times, I invented a term for it - "trace chasing." A guy would set out his scope and start looking for noises. He'd keep turning up the V sensitivity, and sure enough, eventually he'd find something on his screen. Probably just a radio station across town, nothing audible, but there it would be.

Same thing from caps. I am sure some demonstration can be set up that clearly shows something or other, but does it sound any different?

This whole shoulding thing bothers me. When that cap connects a plate to a grid, both ends are active in the circuit. SO then just what is being shielded from what?

[defaced]

I started to mention that, but I've heard conflicting opinions on whether it actually makes a difference at audio frequencies...

Which is exactly why I used very soft language, i.e., may, probably, etc. I have never bothered with outer film. I'm lazy, but I'm more than willing to make work for other people

[Chuck H]

I've heard that the Vishay 715p caps have the label oriented to indicate the outer foil. I had cause two years ago to build two identical amps. All parts were ordered at the same time and some testing revealed the values to be within 1% (same batch run?). So just for the heck of it I built one amp with the caps oriented one way snd the other the opposite way.

The amps sounded identical and there was no difference in noise level. There may be occasions where orientation matters otherwise why would MFG's bother to indicate the outer foil. But for my experience it doesn't matter for guitar amps.

[Enzo]

In my opinion, it matters when you are dealing with RF circuits. It matters when you are bypassing a grid on an IF tube. An oscillator circuit in a tuned RF or maybe some transmitter, they don't need stray capacitance detuning the freq. An extra picofarad can take you out of band in a radio transceiver. But when added to some 0.047uf coupling cap in a Fender, no one would know.