How to rebuild a filter capacitor - Videokarma.org TV - Video

drh4683 · #1 10-04-2009, 12:20 AM

I rebuilt a filter capacitor and took some detail pictures on how to do it and the procedure to do it. The cap show is for Carmines 24NC31 chassis Zenith. Hopefully this helps those who are curious and want to try it out. They're fun to rebuild, like a small puzzle to see how you can make it all work.

http://www.picturetrail.com/sfx/album/view/22501148

***Eric H*** · #2 10-04-2009, 03:37 AM

Doug, very nice presentation, you do neat work.
I never realized the mounting ring was a separate piece, I've always cut it off above the step, I'll have to try this method the next time.

This is such a common subject that comes up I think it should be a Sticky.

Charlie · #3 10-04-2009, 07:51 AM

Yes, that's a great presentation! I haven't tried doing this, but after seeing your steps, I might have to give this a whirl.

Curious... how long does it take you start to finish?

jpdylon · #4 10-04-2009, 09:58 AM

Excellent and tidy work, Doug. Another vote for a sticky.

Carmine · #5 10-04-2009, 11:59 AM

Wow Doug... Fantastic work.

I will admit that I was curious why you went to the trouble of hooking the leads through the bottom of the wafer insulator, until you explained it:

Quote:

Note the leads that were routed up through the wafer board. The goal here was not to solder leads on the opposide side of the wafer. Last thing you want is to solder the wires back to the cap but have the solder melt off the other end where you have no ability to gain access to them.

Thanks for the photostory!

bandersen · #6 10-04-2009, 01:33 PM

Bravo

Yes, sticky please. Perhaps relocate to the Vintage TV & Radio Tech Forum ?

Findm-Keepm · #7 10-04-2009, 02:42 PM

Doug,

I noticed the original 4uF sections were rated at 475V, but the replacements are 450V - can they be de-rated like that in that chassis?

Cheers,

Dan Starnes · #8 10-04-2009, 05:09 PM

What a great teacher you are. I certainly learned somethng new today!

Charlie · #9 10-05-2009, 01:03 PM

Question: If you're rebuilding a can with the cardboard sleeve, the sleeve must remain?

I am working on a can right now that had the sleeve. Under the sleeve, I found the markings on the aluminum can were not the same markings as the sleeve. For instance, the cardboard sleeve showed capacitor values for two sections... a 5 mfd and a 200 mfd. After removing the sleeve, the can underneath showed values for four sections... none of which matched the cardboard sleeve.

At first, I thought they were just correcting the values by covering up the original markings. Then, after looking at the schematic, I noticed the can (serving as the negative side of the capactitor) would have a voltage on it from somewhere further along in the diagram.

Of course, I had to tear the sleeve of my can because it was held on the can with the tar. I suppose I will have to use a toilet paper roll to slide back over the can.

So, if there's a cardboard sleeve, it's important to return the sleeve? Or am just making more work for myself?

DaveWM · #10 10-05-2009, 02:03 PM

I would be very careful to insulated the cap inside the can if you were not going to replace the sleave, worst case some how the replacement cap plastic breaks down, contacts the can, and now you have a hot can exposed.

prob a good idea to put a replace sleave on it anyway just to give a heads up to any future restorer (or yourself) that that can was designed to be hot.

lets say some time later you happen to get anohter good rebuilt can and install it forgetting it was hot and the case on that one is part of the neg, ouch.

when taking those sleaves off try heating 1st.

I just cut the can off and replace only the sleave on those. The sleave will stay put on the bottom of the can base.

Charlie · #11 10-05-2009, 02:10 PM

I would have done things differently had i realized the outer can would carry a voltage.

I'm at the point of crimping everything back in place. Once done, I'll use a TP cardboard roll and electrical tape (for the top) to re-insulate the outer part of the can.

wa2ise · #12 10-05-2009, 07:42 PM

Any hazardous materials in the old caps? Not that I expect to have it for lunch, but do I need to worry about carcinogens?

drh4683 · #13 10-05-2009, 08:00 PM

Thanks for nice words everyone.

As far as the 450 V caps in place of 475, its all ok. B+ on all zenith tube sets is only 390V. There is no surge voltage to be concerned with during initial power up, so its still safe with a good safety factor.

As far as the hazards of the caps, yes, it is a legitimate concern. I have thought about this myself but am currently unaware of any hazardous substances. Im unsure if the electrolite contains pcb's. Perhaps Brian might know in more detail.

Findm-Keepm · #14 10-05-2009, 08:21 PM

Hard to say - the chemical composition is often a closely guarded proprietary formula, but the NIH and others asked for a list of ingredients when Electrolytics started being used as energy storage devices and they grew to enormous size (think industrial UPS'es, braking capacitors in large moving vehicles, and the like)

Here's a page from the NIH whitepaper - the ammonium salts are the most commonly used and have a low-to-medium toxicity. Surely handling a can capacitor's contents with gloves is warranted, and given the infrequent handling, it may not pose an immediate threat. I'm no chemist or safety expert, but I wouldn't go handling these without some caution.

bandersen · #15 10-05-2009, 08:55 PM

Quote:

Originally Posted by Charlie

Question: If you're rebuilding a can with the cardboard sleeve, the sleeve must remain?

I am working on a can right now that had the sleeve. Under the sleeve, I found the markings on the aluminum can were not the same markings as the sleeve. For instance, the cardboard sleeve showed capacitor values for two sections... a 5 mfd and a 200 mfd. After removing the sleeve, the can underneath showed values for four sections... none of which matched the cardboard sleeve.

At first, I thought they were just correcting the values by covering up the original markings. Then, after looking at the schematic, I noticed the can (serving as the negative side of the capactitor) would have a voltage on it from somewhere further along in the diagram.

Of course, I had to tear the sleeve of my can because it was held on the can with the tar. I suppose I will have to use a toilet paper roll to slide back over the can.

So, if there's a cardboard sleeve, it's important to return the sleeve? Or am just making more work for myself?

I've discovered a few capacitors where the sleeve markings and the capacitor didn't match. Always the cap has been lower in value than it should have been. Frugal/cheap repairman ?

I made a few replica sleeves from TP rolls recently. I cut a disc from some card stock for the top. Then cut a few narrow rings from a TP roll and cut a section out so they'd be slightly smaller in diameter. I glued those smaller OD rings into one end of the roll and then the disc. Finally, little black spray paint.