21CT55 #2628 restoration

[Zenith6S321]

All of the original chassis mount caps tested open, leaky, or way off value. The "modern" (1977-ish) replacements that I had tacked in, way back then, all reformed nicely. I am not going to trust them, so I have started re-stuffing the old electrolytic caps with 105C caps. Here are some pictures of a few of them being re-stuffed. I have all but one of the chassis mount cans re-stuffed and I have started wiring them in. The 2700 pF door knob capacitor arrived and I think it will fit in the HV cage well.

[ohohyodafarted]

Nice job on the re-stuffing!

I also use the same method, removing the can from the chassis and pealing back the rolled edge of the can to remove the tab ring. I much prefer this method over the method that cuts through the aluminum can above the base of the can. It's a lot more work using this method, but this method retains the original can in one piece, pretty much un-molested. And when re-installed on the chassis, it is hard to detect that it was re-stuffed.

[Zenith6S321]

On my first attempts I was using a small pair of wire cutters to pry the edge up. It was pretty easy that way, but left ugly marks on the outside of the wider ring at the bottom of the can. With the right small jewelers flat blade screw driver I can force up the edge and then wedge it in, applying pressure along the circumference and then pry up a very short bit at a time. It gives a nice result but is tiring on the hands.

Dave

[ohohyodafarted]

Originally Posted by Zenith6S321

On my first attempts I was using a small pair of wire cutters to pry the edge up. It was pretty easy that way, but left ugly marks on the outside of the wider ring at the bottom of the can. With the right small jewelers flat blade screw driver I can force up the edge and then wedge it in, applying pressure along the circumference and then pry up a very short bit at a time. It gives a nice result but is tiring on the hands.

Dave

I use an old Stanley scratch awl with a wooden handle. I have it ground and curved the tip in such a way that I can work it under the rolled edge and use it to "roll" the edge open once I have it started. Then after I have the tab ring removed. I use a piece of water pipe just the right size, clamped in a vise, as a curved anvil. I take a small ball peen hammer to flatten the unrolled aluminum edge against the pipe anvil. You need to be careful with the awl so you don't slip and run the point into your hand when working the rolled edge open.

[Zenith6S321]

Re-stuffed the last electrolytic after the parts came in. This one is the 1000uF 3V non-polarized cap. Here are some pictures of before, cover un-crimped, the parts, back together, and back in the set. I did this for the other little electrolytics except for three that I did not have the original caps to re-stuff. I wet the paper cover before I uncrimp the end to try to keep the paper from crumbling.

[Zenith6S321]

My selenium rectifiers had been replaced by the time I bought the set. They had been replaced with the 5A 600PIV silicon rectifiers as shown in the first picture. The original(?) soldered-in-fuses were blown and snap on fuse holders with replacement fuses were used. This mess is kinda hidden by the rectifier cover. The plug-in dropping power resistors still measured ok, but I decided to replaced them with chassis mount power resistors. I also wanted to add the recommended 7.5 ohm dropping resistor to match the drop from the selenium rectifiers. And I wanted to put in chassis mount fuse holders. So I rewired it all. Here are pictures before and after all the changes.

[Zenith6S321]

I wanted to test the power supply rewiring and cap re-stuffing. The power cord was intermittent, the chassis mounted cheater socket removed, and the cheater cord cut and soldered in. So I removed the kludge and replaced the chassis mounted cheater socket. Its now back to factory configuration. I removed all of the fuses expect for the main 4.5A 400VAC supply fuse. I brought the power up on a variac with a dim-bulb while measuring the 400VDC supply rail across the 80uF 450VDC cap. At about 300VDC I saw the dim-bulb flicker brighter, heard a "pfffft" sound from under the chassis and smelled smoke!

I cut power and turned the chassis upside down. After not finding anything really wrong, I brought the power back up and saw the source of the smoke. The phenolic insulator of one of the voltage doubler capacitors had carbonized and was heating/burning/smoking intermitantly. The voltage on that capacitors' case is at 200VDC, so there is 200VDC across the phenloic insulator. I guess that's why I removed that cap from the set so many years ago. So I removed the re-stuffed caps' ground wire from the can ground lug to remove the 200VDC across the carbonized insulator and then wired the re-stuffed caps' ground directly to the other voltage doubler capacitor. Here are some pictures. Its all better now.

Now to start the long process of replacing all the paper caps and out-of-tolerance resistors....