I am embarrassed to admit, that after recapping old radios for some time, to learn there is such a thing as a Safety Cap. Probably because we don't use them on the planet I'm from.
I read a bit about them and understand what X2 is as opposed to a Y2 (sorta), but am not sure how they might be used in the Philco 60. I do see, on the schematic, a 0.015 uF cap from one leg of the line voltage to ground. I guess this is an example of a line to ground.Would that be a safety cap, and are there others? If I could have them pointed out on the schematic, then maybe I would better understand them. I completed an old RCA radio repair course, but don't recall any mention of them.
This link should be to schematics of the 60. The December version is the one I am working from.
http://www.philcoradio.com/tech/60evol.htm
Sorry for the long post.
lyle
Yes, that 0.015uF from the AC line to ground should be a Y type safety cap and it's the only one in this set. Safety caps are designed to fail safely (i.e. not burst into flames or explode!) if there is a power surge.
Back in the days when they designed and built these radios there were no such thing as safety caps. They just used the same old paper caps as used in the rest of the radio circuits.
Thank you, so much! I have spent years trying to figure this stuff out by myself. I can't tell you how nice it is to have knowledgeable folks like you to check with. I hope someday I can do the same.
lyle
(03-01-2012, 08:48 PM)bandersen Wrote: [ -> ]Yes, that 0.015uF from the AC line to ground should be a Y type safety cap and it's the only one in this set. Safety caps are designed to fail safely (i.e. not burst into flames or explode!) if there is a power surge.
Back in the days when they designed and built these radios there were no such thing as safety caps. They just used the same old paper caps as used in the rest of the radio circuits.
Or you can move that .015 uf cap to the radio side of the power switch and not worry about whether it's a safety cap or not since it will no longer be energized while the set is turned off. The only reason it's there is to block noise from the power line, RCA and some other makes did not bother using them on their sets since they used an electrostatic sheild inside the transformer.
Regards
Arran
(03-02-2012, 12:23 AM)Arran Wrote: [ -> ] (03-01-2012, 08:48 PM)bandersen Wrote: [ -> ]Yes, that 0.015uF from the AC line to ground should be a Y type safety cap and it's the only one in this set. Safety caps are designed to fail safely (i.e. not burst into flames or explode!) if there is a power surge.
Back in the days when they designed and built these radios there were no such thing as safety caps. They just used the same old paper caps as used in the rest of the radio circuits.
Or you can move that .015 uf cap to the radio side of the power switch and not worry about whether it's a safety cap or not since it will no longer be energized while the set is turned off. The only reason it's there is to block noise from the power line, RCA and some other makes did not bother using them on their sets since they used an electrostatic sheild inside the transformer.
Regards
Arran
Thanks, Arran.
The nice thing about this Phorum is that you not only get an answer, but learn something as well. Being an info junkie, I really like that.
Thanks again,
lyle
Quote: Or you can move that .015 uf cap to the radio side of the power switch and not worry about whether it's a safety cap or not since it will no longer be energized while the set is turned off.
Should it not still be an AC rated cap? If you make that switch and it has failed shorted, you still wind up a loud noise going "bump in the night".
(03-08-2012, 03:41 AM)TexMac Wrote: [ -> ]Quote: Or you can move that .015 uf cap to the radio side of the power switch and not worry about whether it's a safety cap or not since it will no longer be energized while the set is turned off.
Should it not still be an AC rated cap? If you make that switch and it has failed shorted, you still wind up a loud noise going "bump in the night".
How is a cap going to short out while it is open circuit at one end? If it is going to short out at all it will likely be while power is across it and that means the set will have to be on. I'm sorry but this whole safety cap arguement is getting old, I've owned over a hundred sets now, serviced almost as many, and I can't remember finding one with a shorted line cap even original ones. On the other hand I have had bypass caps blow in several sets and encountered shorted filter caps in even more, all were old ones of course. Also I've never had one I replaced fail, they were modern poly-film caps rated at 630 VDC, not AC rated but non polarized and more then ample for the job, if they were connected across the line full time then I would use a safety cap.
I've seen sets where the line cap blew but none that I owned or worked on, even witnessed it happen once, the set was turned on, cap went bang, blew the breaker, then went open circuit. Ironically this was in a 1950 Philco, and one leg of the line cap was on the radio side of the switch, nothing happened until the switch was turned on and both sides of the cap were energized. So one incident in one set in 20 years involving an original line cap and it wasn't my set nor was I working it, they are hardly the tinking time bomb they are made out to be. Use them if you like but to me it's kind of like wearing a crash helmet while driving a car.
Regards
Arran
Quote:If it is going to short out at all it will likely be while power is across it and that means the set will have to be on. I'm sorry but this whole safety cap arguement is getting old
Agreed, sort of. You will note I did not even use the words "Safety Cap". I think that terminology implies something that does not exist. And I have used a lot of high voltage caps in that application just as you have in the past because I did not even know they existed and I just replaced in kind. My old Elmer did, however, tell me I should up the voltage rating. But for a few cents more, why not go first class since they are now commonly available. If it fails open when you power up, you have not really lost anything but the cap. If a common DC cap fails shorted when you power up and the AC hits it before you put the chassis right side up and in the case, it seems to up the odds of losing an eye. I have not, then, saved even the slight cost difference by using a cheaper cap. I am still going to have to replace it when I get out of the hospital. I would hate to now be penny wise and pound foolish just because it never happened to me in 50+ years of doing otherwise.