Non-polarized to polarized?

[TarheelTechinTraining]

I'm looking to replace a couple of non-polarized caps with polarized caps. Is this safe to do or no? The values are the exact same and I have them on hand is why I'm asking. Thanks in advance,Greg

[g1]

Not in that way. You have to make a non-polar out of 2 polarized electrolytics back to back. There was a discussion here about it recently, can't remember where.
The negative ends of the 2 caps are connected together, each cap needs to be double the capacitance of the value you want.

[tedmich]

non polarized (NP) caps are usually electrolytic caps designed for passing an AC signal, like audio. Thus they are found in (cheaper) speaker crossover networks. Only a few type of caps are polarized, famously standard EL and tantalum caps. Nonpolarized EL caps are often two polarized EL caps attached +/- and are a compromise, but there are millions in various audio circuits where they do AOK. If they need to handle AC they start out as NP caps and need to stay that way.

[bluto]

You didn't say what the value or rating is, but FWIW Radioshack carries NP electrolytics in 1, 2.2, 4.7 and 10 uF, 50 V

[Leo_Gnardo]

I'm looking to replace a couple of non-polarized caps with polarized caps. Is this safe to do or no?

If there's some good reason a non polarized cap was used in the first place, better stick with 'em. And if you must replace, it's safe to use a film cap with voltage rating same or greater. Of course that will cost more and likely take up more space. OTOH your circuit's long term reliability will be enhanced as the film cap's lifetime is generally much better than electrolytic.

There was a trend a few years ago to install non polarized caps as cathode bypass in tube pre circuits. Of course all kinds of positive claims were made. "Tastes better!" "Less fattenng!" Seems to have gone away now.

[tedmich]

Merlin advocated NP cathode bypass caps I seem to remember, but NP EL caps will persist anywhere you need smaller and cheaper, like cross overs
film caps (and air core inductors!) can be HUGE

[TarheelTechinTraining]

Thanks all, the caps are 22uf/50v and are used in the bias voltage of a JTM60. I'll just order some new(same) ones. G-one I saw that thread on back to back caps to make a NP cap from polarized.

[Enzo]

Just get something real. These caps couple the AC from the power transformer into the rectifiers of the bias supply.

[Leo_Gnardo]

Thanks all, the caps are 22uf/50v and are used in the bias voltage of a JTM60. I'll just order some new(same) ones. G-one I saw that thread on back to back caps to make a NP cap from polarized.

If they're being used as Enzo describes, you're much better off with film caps.

I take non pols as a poor substitute for film, to be used only in the cheapest speaker crossovers or in circuits where polarity is unpredictable.

[The Dude]

The caps the OP is referring to are actually coupling AC- not filtering it. Here's a link to the schematic. (see lower left).

http://www.drtube.com/schematics/marshall/j600-61-02-1.gif

Edit: You got me Leo! I posted this before your edit. That said, I agree. Film caps would be better here.

[Leo_Gnardo]

The caps the OP is referring to are actually coupling AC- not filtering it.

Thanks Dude! I changed my post to address that. Whoops. Marshall must have thrown caution to the wind, but we're used to that by now.

[J M Fahey]

Well, those are voltage doublers, probably fed from some windings designed to eventually get +/-15V DC for preamp, loop or reverb.
And they do not NEED to be NP, a couple standard/polarized 22uF x 50V will be very happy there, connected with the negative terminal towards the D113/114 anodes, or D109/110 cathodes.
Positive terminals towards the transformer windings .
Donīt think they will suffer more than any other voltage doubler circuit and film caps, although "better" are probably wonīt fit anyway.
2 x 22uF caps in a film version wonīt be small or cheap, thatīs for sure , and probably wonīt even fit.

[TarheelTechinTraining]

Thanks again. I see now that they are AC coupling caps. JM you are right a film cap at 22uf seems scarce at the least. I'll just use the polarized caps I have. Again thanks for the clarification ,Greg