Non-electrolytic Cap Polarity

[Motterpaul]

Is this a thing I should pay attention to? Or is it just voodoo and an oddly badly made cap? Generally, I would only use these in a tube amp or maybe a pedal.

 

[HotBluePlates]

Is this a thing I should pay attention to? Or is it just voodoo and an oddly badly made cap? ...

It is a real thing that may have an impact in an amp.

Simply put, the outer foil in a cap can be used as a partial shield if the cap is oriented in a direction that connects the outer foil to the lowest impedance-to-ground.

How Much effect it has, and whether it is worthwhile to bother with, is an amp-specific question. Overall it won't make your amp "sound better" but it may help reduce extraneous noise. If the amp sounds better as a result, it is due to reducing the influence of that extra noise.

 

[Motterpaul]

OK - that is what they said and I wanted to check with someone with more experience than myself - so thank you immensely for your input.

It is a logical thing, I just wondered why I never heard about it before, but I suspect it has more to do with high voltage tube amps than pedals where I really cut my teeth electronically.

 

[Motterpaul]

Another question, though. Did Fender and Marshall follow this technique back in the '70s when they built amps? Or should one go back and check every cap if they have a hum problem?

 

[Jeff Gehring]

If an old Fender has a hum problem, you won't fix it by reversing a coupling cap's connections. That I can guarantee. (Unless the cap had a bad solder joint to begin with!)

 

[Jeff Gehring]

I think the 60's Fenders adhered to advantageous orientation of the outside foil leads on caps. I think this is chiefly because the blue tubulars were clearly marked for orientation. When Fender moved on to the blue and brown blob caps, those markings went away, and it was not at all worth it for them to try to determine cap outside foil orientation.

For instance here's a '66 Tremolux:

Going from left to right, we see appropriate orientation for all the blue tubulars: those that are attached to a tube's plate have the foil end connected there, and on the non-driven side of the phase inverter, we see its grid cap has the foil end correctly oriented towards the lower impedance point in the cathode string.

 

[Motterpaul]

I think the 60's Fenders adhered to advantageous orientation of the outside foil leads on caps. I think this is chiefly because the blue tubulars were clearly marked for orientation. When Fender moved on to the blue and brown blob caps, those markings went away, and it was not at all worth it for them to try to determine cap outside foil orientation.

For instance here's a '66 Tremolux:

Going from left to right, we see appropriate orientation for all the blue tubulars: those that are attached to a tube's plate have the foil end connected there, and on the non-driven side of the phase inverter, we see its grid cap has the foil end correctly oriented towards the lower impedance point in the cathode string.

Interesting. Thanks for pointing that out. I need to check for markings on my Marshall 2204.

 

[Motterpaul]

My Marshall has the polyethylene caps mostly oriented in one direction. Two are the opposite but they seem to follow the flow so negative is to the out.

I have one film cap that looks exactly like the one in the video and it seemed to be placed properly. You can see a manufacturer's light black line all the way around the negative end - and my orientation based on the markings is just like the one in the video.

I did end up reversing one small film cap (500p) that gave me buzz when I touched it. The buzz did go away.

 

[HotBluePlates]

Another question, though. Did Fender and Marshall follow this technique back in the '70s when they built amps?

I think the 60's Fenders adhered to advantageous orientation of the outside foil leads on caps.

I would extend this to the 50's Fender amps as well. The Red & Yellow Astron caps had the outer foil marked, and the few amp photos I just checked all showed those coupling caps oriented in the correct low-impedance direction.

Checking photos of my two brown Deluxes, I saw something curious. Look at the board from the tube-side of the chassis, the caps in the trem oscillator (laid side-by-side) had the outer foil Towards - Away - Towards the the viewer.​

​

When you compare the layout to the schematic, it shows these caps are connected end-to-end. All of the caps had the outer foil oriented away from the oscillator's grid (and 1MΩ resistor) and in the direction pointing to the oscillator's 220kΩ plate resistor (which runs to a.c. ground at the filter cap).​

​

This could be viewed akin to "shielding the signal path" from plate to grid of the oscillator. Now it wouldn't be terribly effective, because the "shield" is broken into 3 sections along the way. And we really don't care, because shielding for an oscillator is not really a priority. However, it does show someone stopped and thought about "following the rule" here.​

​

62 Deluxe Cap Orientation​

63 Deluxe Cap Orientation​

 

[J M Fahey]

OK - that is what they said and I wanted to check with someone with more experience than myself - so thank you immensely for your input.

It is a logical thing, I just wondered why I never heard about it before, but I suspect it has more to do with high voltage tube amps than pedals where I really cut my teeth electronically.

Answered on post #2 but to add a little, it´s not a "voltage" problem but one of "impedance"

Tubes have VERY high impedance inputs (grids) so it pays to protect them from external hum (nothing drastic but every bit helps)

And the practice comes from the Radio guys, where it DOES matter.

Radios have *microvolt* sensitivity (match that, high gain guitar amp ) and frequency response to many MEGA Hertz (again )

But ... but .... who cares about Radios anyway?

Mind you, Radio was **THE** hot exciting stuff in the 30´s and 40´s, so much so that Leo Fender´s first Company and shop was
called Fender Radio Service:

 

[Motterpaul]

Answered on post #2 but to add a little, it´s not a "voltage" problem but one of "impedance"

Tubes have VERY high impedance inputs (grids) so it pays to protect them from external hum (nothing drastic but every bit helps)

And the practice comes from the Radio guys, where it DOES matter.

Radios have *microvolt* sensitivity (match that, high gain guitar amp ) and frequency response to many MEGA Hertz (again )

But ... but .... who cares about Radios anyway?

Mind you, Radio was **THE** hot exciting stuff in the 30´s and 40´s, so much so that Leo Fender´s first Company and shop was
called Fender Radio Service:

Thanks for the background. I did not realize tubes have such high impedance. (EDIT: I guess I did know - because they seem to be about the same as pedals, like 1M).

I am aware of the radio guys, plus all the HAM operators, shortwave, and all those DIY kits like Heathkit that people used to make.

Replacing tubes used to be something every dad knew how to do. Except for mine (heh). He was useless with tech.

 

[smolder]

There is a story about Kimock and one of the guys at Two Rock taking two identical amps and placing caps through those amps in opposite directions. As I recall, they observed a noticeable difference. The thread further describes a method for determining the shield end without a scope. It might have been here on these forums. Might be worth a search.

 

[Motterpaul]

There is a story about Kimock and one of the guys at Two Rock taking two identical amps and placing caps through those amps in opposite directions. As I recall, they observed a noticeable difference. The thread further describes a method for determining the shield end without a scope. It might have been here on these forums. Might be worth a search.

There are a few YouTubes with some DIY kits people make to determine this with a DMM.

Also - off-topic. I am not well-connected in the amp building world. I didn't realize Kimock was with Two Rock. I have a Studio 35 Reverb. It amazes me that they can make such a great sounding amp at a fraction of the size & weight of a Marshall.

 

[Motterpaul]

There is a story about Kimock and one of the guys at Two Rock taking two identical amps and placing caps through those amps in opposite directions. As I recall, they observed a noticeable difference. The thread further describes a method for determining the shield end without a scope. It might have been here on these forums. Might be worth a search.

I went looking for this, couldn't find it.

 

[smolder]

I went looking for this, couldn't find it.

a search through my bookmarks has it from feb of 2012 on rukind.com. Apologies for not recalling it precisely. The thread has since been deleted (weird), but I did capture this... it’s not coming from me first hand, so a grain of salt...

“Kimock told me that he and Bill at Two-Rock did two identical amps but one amp had them the "right" way and the other ...“

 

[Motterpaul]

a search through my bookmarks has it from feb of 2012 on rukind.com. Apologies for not recalling it precisely. The thread has since been deleted (weird), but I did capture this... it’s not coming from me first hand, so a grain of salt...

“Kimock told me that he and Bill at Two-Rock did two identical amps but one amp had them the "right" way and the other ...“

No apologies needed, I read a lot of good stuff on the way there. Thanks for the update. That was all I needed to know anyway.

 

[HotBluePlates]

... The thread further describes a method for determining the shield end without a scope. ...

There is a non-scope method being shown in the OP video:

if you connect the cap to the input of an amplifier, and hum is loud when you grasp the body of the cap, the Hot lead is connected to the outer-foil of the cap. Hum will be less when the outer foil connects to the ground connection of the amp's input.​

There is a story about Kimock and one of the guys at Two Rock taking two identical amps and placing caps through those amps in opposite directions. ...

a search through my bookmarks has it from feb of 2012 on rukind.com. ...

The outer-foil discussion was "a thing" about a year or 2 before that post. There was some discussion & testing of it on the Hoffman Forum.

I never stop being amazed how many ideas for features or modifications we discussed there (and other places, as members were on multiple forums) made their way into production amplifiers.

 

[smolder]

​

The outer-foil discussion was "a thing" about a year or 2 before that post. There was some discussion & testing of it on the Hoffman Forum.

I’m not at all surprised that it preceded me. I was refurbishing amps prior, but only started building in 2007 or so. Thanks for adding the additional references.

 

[Motterpaul]

Yeah, I have run into the Hoffman forums many times in searches in the last couple weeks. That was a great resource, along with Metropolis and TheAmpGarage - which used to be just a news-server thing (what did they call those?). AikenAmps is another that is gone. I never saw it though.

That Hoffman Thread is a great link. Very informative.

 

[Jeff Gehring]

AikenAmps is another that is gone.

Randall's site is still up! Lots of good tech info there.

Aiken Amps site