My Christmas day 9T246 restoration! Almost.....

[bandersen]

I spent a few hours this afternoon trying to reform a dual 40mfd @450 from the 1948 set I'm currently working on. I was able to eliminate leakage but there's another problem I've encountered before. The capacitance is a small fraction of what it should be. I figure the electrolyte has broken down and it's just not doing it's job properly.

So I'm curious - when you guys reform them are you also checking the capacitance and is it within spec ?

[DaveWM]

yes, and the power factor as well. For the most part the test well over like 50%, if it was under I would reject it outright. I like to compare them to new caps, they generally test higher value, about the same in power factor, and up to about 2 to 4 times the leakage (but its still very low). I used to have a chart that was used for acceptable leakage.

It would not be uncommon for me to take more that 24hrs for one section. Is this really needed, maybe not but it cant hurt to try and besides like I said before it appeals to my interest in experimenting.

What I would really like would be a test setup that I could program to step up the voltage based on current, say have it ramp up to try and maintain a set constant leakage current (selectable), then graph that voltage over time and set the max voltage to end the test. The resulting curves would be fun to examine.

you could do it with a constantly variable DC power supply and a current meter (analog would be easy to watch) but I dont really want to stand by the PS and work that for however long it may take.

[DaveWM]

all the sections seem to have responded well to reforming. I will set it aside and check it in a couple of weeks.

[Kamakiri]

While I understand the premise behind reforming the electrolytics, if you've got a set that you actually want to watch, isn't it easier in the long run just to replace the stupid things?

[DavGoodlin]

Just like WA2ISE, I have a box full of removed multi-section cans. A few weeks ago, I tested them on my EICO 950. Almost every one of them had at least one open or leaky section. While the open caps are done for, the others could be reformed. Having never heard of reforming before following VK, I have RCA 721TS and 8T241 that I could try this on when I finally get to them. I also plan to fuse them pretty tightly as well!

For sets that are not what we consider "classics" and most of my 30's radios, I generally leave the old ones in, disconnect and solder new ones under the chassis. If someone has the time to refrom or restuff them in the future. At least they look original from the top.

[M3-SRT8]

Now you see 'em...



Now you don't...

[Penthode]

To further belabor the reforming of an old electrolytic capacitor discussion , the reforming takes time, especially if the capacitor has remained dorment.

Last year, when I restored an RCA 9TC275 (1949 with a 16AP4)) according to the original owners, the set had sat in a basement since 1964 un used. This set was a good test case as someone plugged in the set and melted one of the 5U4's literally!!

I was curious if the capacitors could be revitalized after this abuse. I found all the electrolytics almost a dead short. I left in position each electrolytic can on the chassis and isolated the connections to individually test each capacitor. I used my Sprague TO-6 to reform the dielectrics one-by-one. Each electrolytic section took about two to three hours to reform. After replacing all the paper capacitors and a few other components (mostly bad tubes and resistors) I ran the set on the bench for a couple of weeks, keeping an eye on the electrolytics. A 40ufd section of a multi-section capacitor opened and i replaced it with a new old stock multisection unit (after reforming it). I now use the set almost daily and it is reliable without any capacitor issues.

What must be remembered is that even the dry electrolytics have a healing property. The crumbliness when disassembly is normal and does not necessarily mean the capacitor is bad.

Incidently, I am still working on my CTC5 and it was another long time dorment set with shorted electrolytics which reformed nicely apart from two Canadian Mallorys which was part of the Canadian 25Hz modification. The US RCA original capacitors all restored fine and are healthy with leakage below 100uA at full rated voltage.

I would encourage all to consider at least testing the components before condemning them.

Saying that, I have also done my share of restuffing over the years. My method is to slice the can about half an inch higher than depicted above. That is, about 1/2" above where the can becomes larger in diameter. I then obtain short section of aluminum tube slightly larger in diameter than the electrolytic and cut a 1" length. I then carefully slice it to remove a longitudinal section to reduce its diameter just enough to ensure a force fit on the inner diameter of the old electrolytic tube. I install new internal capacitors and then press fit with a vice the capacitor back together over the prepared 1"section of tube. The result is clean and barely perceptible from the original.

[DaveWM]

Originally Posted by Kamakiri

While I understand the premise behind reforming the electrolytics, if you've got a set that you actually want to watch, isn't it easier in the long run just to replace the stupid things?

easier... maybe but not by much. I just disconnect the leads and hook up the variable power supply. after that I just walk away and check on it now and then. If they check out I reconnect the wires and its good to go.

I have MANY sets that are daily drivers, examples are my predicta and portacolor, the predicta had one bad can cap, the one with a low volt high value. the other two (a doubler and a mutisecion can that lays down in the back) checked out fine. I use it daily and its fine.

the porta color has its orig caps (1972 IIRC) its on for hours everday and I have had no problems at all with it.

I have a zenith CCII same story, and many sets from the 60's same deal.

I do of course come across bad caps, and when they test bad I replace them, but I do not just wholesale replace, I just dont see the need.

Besides frankly I sometimes wonder if the new caps will last any longer. I am not saying its right or wrong but it works for me.

When I do find a bad one, I use a bone saw, cut the can off at the shoulder, use a pin vice to drill holes from the bottom up, then put tall skinny radial caps in and solder them to the existing can terminals. Takes about 5 min per section so its fast, and I leave the orig lead dress alone. if there is a cardboard cover I will just put the now empty alum can back on and use the sleeve on to hold it, if no sleeve I use a little bit of 5 min epoxy around the edge (after cleaning it up).
The down side is the epoxy is not that strong a joint, so if at some time in the future, someone grabs the can like a handle for the chassis they may be in for a big surprise when it lets go.


after reading Pentodes method of using an expanding internal sleeve I will have to give that a try.

I have tried the uncrimp method, but that just takes a bit more patience than I have. the bone saw while crude is easy and quick.


I promise no more reforming on this thread, I don't want to come across as a zealot.

[Zenith6S321]

Originally Posted by DaveWM

What I would really like would be a test setup that I could program to step up the voltage based on current, say have it ramp up to try and maintain a set constant leakage current (selectable), then graph that voltage over time and set the max voltage to end the test. The resulting curves would be fun to examine.

I threw together what you described above from Radio Shack stuff. It uses an Arduino Uno and a pulse width modulated motor controller to drive two 12.6V to 120V filament transformers to step up to 240VAC. Then a voltage quadrupler. This results in a programmable 6-900 VDC supply, The Arduino software reads the analog inputs to raise the capacitor voltage while limiting the current and max voltage, and then monitoing the current decline to the required minimum current. Anyway, here are some plots from four capacitors. I set the current limit to 5 mA, and the voltage limit to the cap working voltage. The first cap is a 630TS 40uF 450V, the second a Sprague 16uF 450V cap added as a repair, the third a 630TS 80uF 150V cap, and the last a Nichicon 82uF 450V cap. My Sencore LC75 says the RCA caps show a lot of dielectric absorption, the Sprague is toast, and the Nichicon was the best (of course, its new) but did also show some dielectric absorption. I thought it would be interesting to plot the computed power going into the cap as well as its computed effective resistance along with the measured voltage and current. Although its now controlled through USB, it could be standalone with the addition of a small two line LCD panel and some switches. I think I could save some of my 630TS caps, but some are completely unresponsive to reforming.

[DaveWM]

interesting graphs, would like to see both graph at 200 seconds. for 1 and 4

Also if you reran the test on the old caps does the graph change (reformed) so the low current target at rated voltage is reach sooner.


I looks like the 82uf took that long to hit max voltage, perhaps for reforming you could ramp down the current to say 1ma max. Very neat project.

[Zenith6S321]

Originally Posted by DaveWM

interesting graphs, would like to see both graph at 200 seconds. for 1 and 4

Here is a plot of 1 up to 250 seconds. Is that what you mean?

[Geist]

Hi All;
I would like to see a circuit diagram ?? So, I can build one as well ..
THANK YOU Marty

[Einar72]

And the SW for the Arduino...

[cbenham]

Originally Posted by M3-SRT8

Now you see 'em...

Now you don't...

Does anyone know if the black cardboard tubes you have used are available anywhere new or even new old stock?

I used to see them in the mfgr.'s catalog and in the radio supply stores but
no more. Seems like these would be a good sale item for restorers.

Cliff

[Sandy G]

Caps are cheap, why trust a nice old set to 50, 60 yr old caps that MIGHT have reformed, or maybe are just "Playin' Possum", as it were ?!?