I do a lot of AA5 restorations and these typically have a 0.1uf cap from B- to the chassis.
They also, usually use a 0.1uf or a .05uf cap for the AVC.

I got to thinking about the price of a 0.1uf cap @ 630vdc. They cost anywhere from 50 or 75 cents to a $1.

Then I realized that ( as long as you use a polarized AC plug on the power cord) there is so little voltage across either of these two caps that 630v rating is just ultra-super overkill ... lol

So I found 0.1uf @50vdc caps will work absolutely fine and these will only cost about 1 cent each for ceramics.

Try it.

This will backfire on you the first time someone plugs in to a mis wired socket and they can fail shorted and kill someone. In any case safety caps should be used.

No it won't "blow" the cap if the plug is simply reversed.... not unless there is a voltage potential greater than 50volts across it.
That can only happen if the metal of the chassis is somehow outside of the insulated plastic or wood cabinet AND/or if it also is somehow accidentally or purposely physically electrically connected to EARTH ground or neutral.

Simply plugging the polarized plug into a (some-how) mis-wired outlet cannot (in and of itself) cause a problem.

Several events would have to occur ALL at the same time.
1.) A mis wired socket
2.) The chassis being exposed
3.) the exposed chassis connected to neutral or earth.

I don't disagree at all, I just wanted to point out that nobody should bet their life that the socket is properly wired. And this does not only apply to very old homes, I've seen some built within the last 10 years that are totally messed up. Really.

A one cent cap is virtually free.
Even if I did a hundred AA5 restorations per year....I'd find a way to absorb or recoup the cost of one additional cap.

It's not "overkill" to properly insure the safety of consumer equipment.
In my work, I do not cut corners.

There's no problem with using a 50 volt cap on the AVC line where the voltage is never going to reach that point. At the time most of the tube radios were made, the lowest commonly stocked voltage rating for paper caps was 200 volts.

The cap from B- to chassis, however, is another story. There is some danger of that one shorting out should the chassis be grounded either on purpose or by accident. As already pointed out you can't trust outlets to be correctly wired. That particular cap needs to be rated at least as high as the original was, and last time I checked 630 volt caps weren't expensive in values of .05 or .1, especially if you order them in quantities like most of us do.

Basically... You're right... and I am usually the LAST person to ever even think to try to save a few cents...
But I was repairing a radio recently and saw that I was almost out of the 0.1@630v.. and started to think about what was the "actual" voltage across this chassis coupling cap and the AVC cap.. and so it was just a logical thing.
so.. I started using some nice new style 0.1uf@50volt caps that I'd gotten on a strip for practically nothing.

My reason for the "tip" primarily was to remind you that sometimes if we actually stop to think about what the circuit is actually doing in certain areas... we can use our noggins and only use what's really needed.

Of course you are right. I have a box of very good quality 50 volt ceramics in 25 mostly small values which I got for practically nothing, and use them freely to recap sets where there is little or no reason to use anything else, i.e. shunted to coils with a few ohms resistance, etc. Any doubt I don't go to that box. Everything else gets 630 volt orange drop types or 500 v/1000 ceramics. Only keep 450 VDC filter caps around anymore, except for ridiculous 25 VDC values for DC filaments, and stuff like that.

Likewise I bought probably 500 pcs (or almost a full reel) of Nichicon electrolytic caps ( 22uf@25v) for only about $10.
A real bargain..
So ....I always use these now to replace the cathode by-pass on the output tubes (35L6, 50L6) where the voltage is only about 5-6vDC
... probably a life-time supply or more for sure... No?....lol

I buy many of my capacitors from Bob; at 25 per bag, they are fairly cheap.

http://www.radioantiques.com/supplies.html

I'm a high roller. I use Y2 250v disc safety caps for line to ground even though they cost me a whopping 65 cents. If I feel really extravagant I spring for a Y2 film safety cap at 94 cents. I use .01 uF for this application rather than the usual .1 uF originals.

Bob

I normally do not pay retail for parts anyway. However I do not crank out lots of restos on a regular basis to need large volumes. I go to the surplus store in the city and buy caps for maybe ten or fifteen cents each, in some cases. Pick and find at swapmeets etc. However if the vintage or quality of a NOS cap is in doubt, I do have a tester that can check the common characteristics for safety and peace of mind. I also use replacement NOS caps at work that are marked up from 10 to maybe a much larger factor in price. Depending on the market and rarity. Or whatever the supplier chooses to charge. Someone else is buying those, though. Have installed expensive NOS caps with date codes in the 70s, maybe older, that I cannot recall. But after having a NOS lytic short out of new stock and blow up a power supply, I do even test them at work now. Caught the next one that was bad.

If the radio has an external antenna connection, and, the capacitor is connected, along with
a resistor in parallel (~3.3 megs) between one side of the power line and a metallic path back to
that terminal it must be a safety cap.

and the chances of dying from an electrical shock from an AA5 are about a trillion to one

~jeff~

I use RADIAL lead caps almost exclusively in AA5's... they are smaller and cheaper, and make a nicer job. Most caps tie to chassis or a common B- so axial is not needed in 90% of cases, even in big chassis radios... but you have to understand circuitry to know that and most servicers are cap jockies that just replace what they see.

Anyways, .1mfd 630v radials are 32c ea in 25pc bags from a famous capacitor supplier I know very well.

You can really save a lot when using RADIAL lead filter caps. They bundle nicely, and are smaller for stuffing in old cans or under old cans.

Mark Oppat
www.oldradioparts.net

Agree with all. I would rather die from being shot by a jealoous husband, and not from a faulty capacitor. And if I give a set away to the kids or a friend, or a relative, or for that matter anyone on this forum. I care what's inside.

I used to say that, when I was younger. Not much chance of that happening, anymore. But,Just it case, you need to take that pill everyday so that, whenever, whereevr she might be ready, you're ready. Then you take a bath outdoors in separate tubs......
Oh, Oh, I had TOO MANY Smileys! Reduced it to six.

OK Guys -- we're starting to drift off topic here.....



Chuck

I dont understand buying 630V .1 and .05 caps when even 400V is overkill for most replacement use. After awhile the savings add up. Buy the 630V in 25/50 bags as there are times you have to use them.
Ive used 50 and 100V discs on AVC lines and some cathode bypasses, especially in auto radios, since the late 60's as the size reduction makes those sets so much easier to work on. Im still working on 1000 qty bag's of .01 to .1 I bought surplus for about $20 each in the 80's. The same goes for 200 and 400V mylars of the same values I picked up at an auction in 91. All USA made.

When Im forced to buy 600V and higher I deal with a couple of Ebay surplus shops that I now deal with direct. I also get silver micas that way.

Electrolytics are always bought new, mostly from Mouser, although I have bought name brand surplus lots of 25 and 50uF 25/50V.

Carl