what kind of capacitors are these

[Mike Mag]

this is an Adcom GFT-555MK2 tuner and it has a handful of capacitors that look like blue glass surrounding a capacitor
I have never seen any caps exactly like this before.
can someone teach me a bit about them ?

 

[whoaru99]

My guess is maybe polystyrene. Leave those alone.

 

[Mike Mag]

Yes I would guess polystyrene but wanted some expert info. I had no plans to change them just understand them.

 

[Hyperion]

Yes I would guess polystyrene but wanted some expert info. I had no plans to change them just understand them.

The dielectric of these capacitors exhibits very low distortion. For audio or low/medium RF frequencies they are often used, and they would be used more often but for their size vs capacitance ratio (poor compared to others), and/or their sensitivity to heat or solvent damage. The radial construction of the ones in your picture minimises the effects of lead inductance, which is another consideration.

Enough?

 

[Mike Mag]

I am curious why they seem to be enclosed in something like a blue glass drop

 

[gadget73]

Usually the PS caps I've seen are a clear blob, but its just whatever the outer coating happens to be made of.

 

[Hyperion]

I am curious why they seem to be enclosed in something like a blue glass drop

Probably to protect them from the aforementioned solvent damage, I wouldn't lose any sleep over them - just leave them alone.

 

[Mike Mag]

I am very impressed with this Adcom GFT-555MK2 tuner, lots of quality components, sounds excellent on the local jazz station and well built. the only flaw is the trimmer caps in the tuning circuit are not at the highest reliability level

I do not know why most people condemn Adcom tuners, maybe they are prejudiced against them and wont give them a chance. I thought they were bad because of what I read until I gave one a chance and it really impressed me.

 

[gslikker]

I have a few caps looking the same but greenish instead of blue-ish.
They are as low DF as my other polystyrene caps.
The encapsulation must be the polystyrene itself...

The picture looks like it is a quality build piece of equipment.

 

[Lavane]

You see them in phono stages also. In an old thread, someone replaced them with film caps. And yes chastising did occur by some.

 

[rothwellaudio]

You see them in phono stages also. In an old thread, someone replaced them with film caps. And yes chastising did occur by some.

Polystyrene caps are made with a polystyrene film, ie they are film caps.

 

[whoaru99]

FWIW -

Polystyrene as a Capacitor Dielectric
The polystyrene capacitor was the device of choice for precision-tuned circuits due to the extreme stability in the 0°C thru +50°C range as well as long-term stability. The major drawback of this dielectric was the maximum operating temperature of +85°C, the glass transition temperature of ~95°C, and a fluid temperature of +100°C, making applications for this device limited.

 

[llwhtt]

I just today replaced a bad one in a Sanyo receiver RIAA phono stage. Luckily I had some in my stash, very hard to find today and if you do find them they're back ordered like everything else. I don't even think polystyrene for capacitors is made anymore.

Craig

 

[rothwellaudio]

I just today replaced a bad one in a Sanyo receiver RIAA phono stage. Luckily I had some in my stash, very hard to find today and if you do find them they're back ordered like everything else. I don't even think polystyrene for capacitors is made anymore.

Craig

Yes, I too thought polystyrene capacitors were no longer manufactured. They're very good caps for audio but the small capacitances available mean they can't be used often. Very good in RIAA EQ filters though. Be careful with flux cleaning solvents though - the caps melt!

 

[gadget73]

Polystyrene caps are made with a polystyrene film, ie they are film caps.

"film" covers several dielectrics but people rarely seem to be specific about which one exactly. I'm guessing they usually mean polypropylene but who knows really.

 

[rothwellaudio]

"film" covers several dielectrics but people rarely seem to be specific about which one exactly. I'm guessing they usually mean polypropylene but who knows really.

Yes, "film" is about as specific as saying "stuff". Similarly "poly". Poly-what?

 

[audiodummy]

Poly = Solid Polymer (polarized!) Electrolytic of course!
Agreed, people shouldn't say simply "film" (are we talking a photo capacitor?!) or "poly" caps, spell out whole word polystyrene, polypropylene, polyethylene terephthalate (mylar), solid polymer, etc., etc. Technically I'm okay with mixing all the plastic capacitors together as they're still fairly similar to each other compared to ceramics or electrolytics, but once the solid polymer electrolytics came on the scene I got up in arms.

BTW they still make paper capacitors right? Think so...at the very least I think aluminum electrolytics still use paper as the mechanical separator.

 

[gadget73]

If you mean paper in the vintage tube gear paper cap sense, one can only hope they do not.

 

[audiodummy]

Appears that Kemet still makes paper capacitors (not counting liquid electrolytic).

 

[rothwellaudio]

If you mean paper in the vintage tube gear paper cap sense, one can only hope they do not.

Yep, paper-in-oil or PIO capacitors are highly prized in some audiophile circles.

https://www.hificollective.co.uk/components/jensen_copperfoil_in_aluminium_can.html

They're also made for commercial, non-audiophile applications such as class X2. These are made by Kemet (as mentioned above).
https://uk.farnell.com/kemet/pme271md6330kr30/cap-0-33-f-10-paper-radial/dp/2495783