capacitors (polyprop) installed backwards?

i am watching this video and wondering about my st70.

apparently caps used to come marked with a stripe indicating which end (outside foil end) should go to the low impedance side of the circuit but the modern orange/brown/greed dipped once dont.

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is this a valid concern in the amount noise injected into the signal path on  my amp?

Modern caps are made differently and do not show the foil side makings. Any cap that you see in old gear that shows the stripe indicating foil side, replace immediately. I don't think Dynaco products are old enough to have those type of caps but perhaps.

this video shows that there still is a foil side on modern caps but that they just arent marked

More fodder for the anal retentive amongst us ...
(come on ... you know who you are!)   ;-}

Unlike electrolytics, the current in these caps crosses the same no matter the direction of travel, and there's no deforming issues to worry about. If there is any minimal difference in what comes out, keep in mind that capacitor tolerances tend to be quite large anyway. Most circuits will fire with no apparent degradation as long as it's within 20% of the design rating. Only real exception that may concern us audio types is tuner circuits where tolerance is much tighter.

Most polys I see in a circuit are there to bypass any residual AC in a line level signal. I use anywhere from .1 to .22 for these applications - any voltage rating that meets or exceeds the design requirements - they all work the same as long as they don't explode.

Still might be fun to take a peek at these ... picked them up to rebuild some crossovers, and I imagine any such issues would be more applicable with the larger values.

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"some claim to hear a difference in the sound quality depending on which way the outer foil is oriented"

Probably the same dummies who think the rectifier can make an amp sound different.

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All I know is in my first refirb I had the bias caps in backwards and the thing lit up like a firecracker. I put orange drops in other positions and there was no pos/neg markings and all went well. Can't tell you the difference or what applications but the electrolytics on the bias circuit were not happy with my mistake.

A lot of the issues with the electrolytics in the bias circuit are due to...of all things...too much experience with electronics! Nearly all unipolar power supply applications are positive-hot, negative-ground, and by instinct and habit, a tech or modifier may tend to wire in those capacitors with the negative side grounded. The bias supply in Dynacos is NEGATIVE so the capacitors must be POSITIVE-grounded.

More people have done this than will admit it!

Don't ask how I know.

sKiZo wrote:More fodder for the anal retentive amongst us ...
(come on ... you know who you are!)   ;-}

Still might be fun to take a peek at these ... picked them up to rebuild some crossovers, and I imagine any such issues would be more applicable with the larger values.

That BATTERY in the lower right corner probably won't work very well...!!!

Don't encourage him.