Exactly What Is A PETP Capacitor?

[Grainger49]

I have some KKs that are K73-16.  They are PETP, but what is PETP?  And how good is that as a dielectric?

Thanks in advance.

[xcortes]

PTFE

[Grainger49]

These don't look like the Russian Teflons, PTFE, they are green on the ends and I believe were sold as PETP.  Sounds like a lot of alphabet soup.

[Paul Joppa]

From Wikipedia:  "Polyethylene terephthalate (sometimes written poly(ethylene terephthalate)), commonly abbreviated PET, PETE, or the obsolete PETP or PET-P..."  Think Dacron sails and polyester Nehru jackets. Also called Mylar.

[Grainger49]

Thanks, I know PET as the plastic in soda bottles.  Mylar I also know but didn't know they were the same stuff.

Were Nehru jackets Polyester?  (remember them well, didn't have one)

Are they supposed to be good sounding caps?

[Jim R.]

Mylar is used in many caps, and even sometimes is also found in the paper of some otherwise labeled paper caps.  I believe the Jupiter HT series is actually a paper/mylar blend of some sort, but it is still described as paper.  I believe only the orginal "wax candle" type Jupiters are the only ones that had a pure paper dielectric.  Also, they now say so, but I suspect that the original Audio Note PIOs -- copper, silver and tin -- also had a paper with a certain percentage of mylar in it.  And of course there are dozens of metalized polyester types.  Auricaps, for example.

Have you given them a listen yet?

-- Jim

[Doc B.]

I think that Auricaps are metallized polypropylene rather than polyester.

[Grainger49]

Jim,

I have used them as power supply bypass only.  I will give them a listen in something soon.

Thanks for the information.  It is encouraging. 

[ToolGuyFred]

I find that the relative permitivity or dielectric constant is often a fair guide to a material's "goodness" for use in an audio capacitor:

Vacuum	1 (by definition)
Air	1.0006
PTFE	2.1
Polypropylene	2.2-2.36
Polystyrene	2.4-2.7
PETP	3
Polyimide	3.4
Paper (unoiled)	3.5
Transformer Oil	4
Mica	3-6
Glass	5-10

(Information from Wikipedia, ElectricianEducation.com and Goodfellow.)

Hope this is useful.

[Jim R.]

Dan is right, I mistated on he auricaps.

John, thanks for the table.  Don't see cotton, silk, or polycarbonate on there -- there are some new caps coming out with polycarbonate dielectric now, but I have no idea how they sound.

-- Jim

[Grainger49]

Fred,

Thanks, I have some air dielectric parallel plate capacitors.  I probably won't try them though. (Picture turned upside down to make more sense)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi244.photobucket.com%2Falbums%2Fgg7%2FGrainger49%2FIMG_0291.jpg%3Ft%3D1293469920&hash=bb88226d26db973ceb3435c078ce367acddd022a)

Good list!  Funny, it follows much of what I have experienced and heard elsewhere.  My true confusion was not knowing that my new KKs were made of old Nehru Jackets (Dacron/Polyester).

[ToolGuyFred]

John, thanks for the table.  Don't see cotton, silk, or polycarbonate on there -- there are some new caps coming out with polycarbonate dielectric now, but I have no idea how they sound.

Can't find any values for silk.

Polycarbonate	2.9
Cotton	1.3-1.4

The polycarbonate & foil caps I have heard were OK but only available in low values.
Cotton will only maintain this value if kept bone dry - some sort of oil or resin would keep the moisture out - but I suspect that would seriously impact the dielectric constant.

[Jim R.]

John,

Thanks, and I am also looking at this from a wire insulation perspective as well.

Lie Grainger, most of this agrees with what I've heard (though have not heard any polycarbonate caps myself yet)  That said, I'm not a huge fan of teflon on wire, but in caps, I do mostly like it.

-- Jim

[Dyna Saur]

Then there are the caps which are not really that  which they appear to be:

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fwww.pastisch.se%2Ffaktiskt%2F20071207-214523.jpg&hash=6693de5e604505a91f32d68886333faf1a019854)

Saw this one  over at the www.diytube.com website

/ed B in NC

[Paul Joppa]

Yow! That's scary.

Speaking of scary, thanks for the link - I didn't know of that site. Under SC35 there's a thread on standby switches in the center tap of the power transformer - exactly what I've been telling people for years based on theory, and nobody every buys it. But it's true nonetheless - switching high voltage DC will destroy switches. Nice to see that experience nears out the theory!