Line to ground capacitor - Videokarma.org TV - Video

ldatlof · #1 08-09-2005, 11:54 PM

Hi. I just got a Westinghouse H-204 AM/FM radio that I want to restore. Because I am a newbie at this (recapped two Heathkit integrated amps) I was reading up on the hazards of AC/DC radios and came across the article that said you should replace the line to ground capacitor with safety capacitors. I am not 100% sure which one is the line to ground cap. I have attached the schematic. I think it is C21 on the bottom left of the circuit.

Any and all help is greatly appreciated. Thanks.

sean · #2 08-10-2005, 08:38 AM

Hi ldatlof,

Yes, C21 is the line to ground capacitor. I had been ordering Vishay caps from Newark but they don't seem to have them in stock anymore. The value of the safety caps used in the sets originally creates more leakage current from line to ground than is acceptable by todays standards. A smaller value capacitor is usually used as a replacement. I have been using the 4700pF cap in the 440L series found on this datasheet: http://www.vishay.com/docs/23092/aclinecp.pdf
Hope this helps.

Chad Hauris · #3 08-10-2005, 08:53 AM

This cap in the Westinghouse is actually a noise suppresion capacitor, not a line to chassis isolation cap...the power line connects directly to the chassis and is not isolated with a cap as many sets of this era are. A safety rated cap would be good to help guard against a short on the filament line though. Also I would install a fuse in the hot lead of the powerline for extra protection, like a 1/2 amp.
Watch out for the volume, tuning and switch shafts and chassis screws as they may connect directly to the hot chassis with no isolation.

ldatlof · #4 08-10-2005, 10:20 PM

Hey Chad and Sean - thanks for the info. My Sam's photofact arrived today and they call the cap a line filter. Not exactly sure what that means. Anyway, this cap (c21) seems to have been working very hard as it is the most damaged looking. The wax is all melted and bubbling.

I tested all the tubes and they all tested good, so I used a variac to power the unit up over 18 hours. The radio is working very well. They really built these radios to last.

I am going to recap and change out the selenium rectifier placing a 100 ohm 10 watt resistor ahead of the silicon diode. There is already a 47 ohm 2 watt (R7) (strange looking resistor - called a rectifier balast in the Sam's) before (ahead of) the Sel. Rectifier. Do I leave it in or remove it?

BTW, to make things more confusing, the Sams says it's 47 and the schematic I attached says its 47K. It has a yellow and black band on it. In between there seems to be some sort of woven fabric. Thanks again.

Chad Hauris · #5 08-11-2005, 07:06 AM

The resistor is not likely 47 K, probably 47 ohms...you can replace it with the 100 ohm 10 watt resistor...make sure you put a fuse in the power line to protect against a short on the new silicon diode.
The old resistor is probably fiberglass but might contain asbestos so just be careful removing it, not to break it apart or cut into it. It is listed in the parts list as a "Glasohm" 47 ohm resistor so the schematic marking must be wrong.

ldatlof · #6 08-11-2005, 05:29 PM

Hey Chad, I followed your advice and replaced the selenium rectifier with a silicon diode. I removed the 47 ohm resistor and replaced it with a 100 ohm 10 watt resistor. I also installed an inline fuse (.5A slow blow). I put the fuse after the silicon diode - I am not sure if that is the correct place for it though. The radio sounds even better than it did before. I am just waiting for the new caps to arrive in the mail and I just be pretty close to done. Thanks.

Chad Hauris · #7 08-11-2005, 09:10 PM

I like to put the fuse in the power line right where it comes in from the cord, before anything...that way if your diode shorts or if you have a filament short the fuse will blow...after the diode it won't give that protection.

ldatlof · #8 08-12-2005, 03:11 AM

Time to rewire then. Thanks.

ldatlof · #9 08-17-2005, 10:19 PM

I have just finished recapping the Westinghouse.

It sounds excellent. I just wanted to thank you both for all your help.

I replaced all the paper & e-caps. I also replaced the selenium rectifier with a silicon diode and added a 500 mA fuse (in the right place this time). I also replaced some resistors that were out of spec.

This was an excellent learing experience and a lot fun.

Thanks again for all your help. Gotta to get back to the Oscar Peterson special on the local jazz station.