[bridkarl]

I’m having to replace this audio coupling cap between the plate of a 6F6 and a phone jack.
The parts list just says .005 20 percent mica which I’m reading as 5000pf. Am I reading that right.

Previous owner put in an .005 electrolytic.

[HowardWoodard]

According to AI, "Yes, you're reading that correctly. A .005 capacitor typically refers to 0.005 microfarads (µF), which is equivalent to 5000 picofarads (pF). The 20 percent mica notation indicates the tolerance of the capacitor, meaning its actual capacitance could vary by ±20%.

Mica capacitors are known for their stability and reliability, making them a solid choice for audio applications. If you're replacing the coupling capacitor, just ensure the voltage rating matches or exceeds the original spec.".

[bridkarl]

That’s what I thought, but when I’m undoing 50 years of “repairs” it never hurts to check. Thanks

[DaleHCook]

Why are you having to replace it? Does it measure out of tolerance? Is it mechanically damaged?

[HowardWoodard]

Not trying to answer for the OP, just commenting on the thread.

According to AI... ...assuming the electrolytic that's in it now is polarized...
--------------------------------------
Using a polarized electrolytic capacitor instead of a non-polarized one for audio coupling can lead to several issues:

- Distortion & Nonlinear Behavior – Electrolytic capacitors are designed for DC circuits, meaning they expect a constant polarity. In an AC audio signal, the voltage can reverse, causing the capacitor to behave unpredictably, introducing distortion.

- Leakage Current & Reduced Performance – Polarized electrolytic capacitors tend to have higher leakage currents, which can degrade the signal quality and reduce fidelity.

- Potential Damage – If the capacitor is reverse-biased, it may break down over time or even fail catastrophically.

- Workarounds – Some designs use two polarized electrolytic capacitors in series (with opposite polarity) to mimic a non-polarized capacitor, but this is not always ideal.

For audio applications, it's generally best to use non-polarized capacitors, such as film capacitors, which offer better frequency response and lower distortion. If space constraints require electrolytics, consider non-polarized electrolytic capacitors, which are specifically designed for AC signals.

[DaleHCook]

According to AI... ...assuming the electrolytic that's in it now is polarized...

What does your response have to do with this thread? The OP was asking about a mica capacitor.

[RodB]

The OP stated that there is an electrolytic in the circuit in place of the coupling cap and wondered what effect it has. Yadda, yadda, yadda. Don't we see this all the time? Someone grabs whatever cap m they may have and IF it works, fine. So there it sits for 60 years. So now we can put the proper part in and listen on headphones. Easy, peasy.

[morzh]

I also was wondering what the post about using polarized caps had to do with the subject?

The cap is 5nF, does not exist in any polarized form....



As for why to replace. I'd be surprised if it was mica, they may come with this range of values, but I have never encountered a 5nF mica cap in the old radios; this value is typically a paper cap.
If it is indeed a mica, as pointed by Dale, if not damaged, it needs not to be touched.
If a paper cap, then it should go.

[RodB]

Maybe it's one of those paper caps that is wrapped in a mica-lookiing case.

[bridkarl]

OP here- the parts list calls for an .005 1000 volt mica. It currently has an .005 1000 volt electrolytic that is at least 40 years old. That needs to go.

I was just originally asking because I always have an issue with math and conversions. My apology for any confusion.

[Radioroslyn]

If this helps you sort it out just remember 10,000 mmfd or pf = .01 mfd. So 5,000mmfd = .005 mfd.