I have been cleaning up my 1950 arvins chaissis up the past 2 days, and had a good full picture almost all the way restored, i put the 5u4 back in, broke the socket! problem solved, turned the set on bbbbbbbbbbbbbbbbzzzzzzz
pop bell top 5u4 dead! one of the very few caps that tested good left in :tears: this is why we do FULL restorations!
also it almost cought on fire! i did get free confetti!

free confetti from a blown filter cap I'm assuming........

Hi All;
Too bad you didn't get it on Video, It would have been a sight to see..
THANK YOU Marty

Good thing it didn't blow into an eye! Been there, done that!

Electrolytic caps can suddenly go crappy on you. I just had it happen to a '64 Zenith AM-FM H845, I tested the 4-section electrolytic OK, but it just started humming a bit more each day and I knew.....I was not done even though I replaced the wax-papers and put a silicon rectifier/series resistor in place of the selenium. should have been first on the list.

I bet the new 5U4 was putting out a bit more EMF..was there a phfffft sound first?

Electrolytic caps can suddenly go crappy on you. I just had it happen to a '64 Zenith AM-FM H845, I tested the 4-section electrolytic OK, but it just started humming a bit more each day and I knew.....I was not done even though I replaced the wax-papers and put a silicon rectifier/series resistor in place of the selenium. should have been first on the list.

I bet the new 5U4 was putting out a bit more EMF..was there a phfffft sound first?

no, but i have heard that sound, this one i was watching, and it made a pop, then a loud hum i go to turn it off, and sparks confetti,(heck of a mess to clean up) and its being taken to grandpas this weekend

i just got done this week recaping my 1955 zenith , i think its the first time iv seen a set that every cap none polerized and electrolytics where all bad ,not one cap was even close to being good most just leaky. it turned out great nice sharp picture ,sound nice and clear ,after going through the tuner its like a new set now.

i just got done this week recaping my 1955 zenith , i think its the first time iv seen a set that every cap none polerized and electrolytics where all bad ,not one cap was even close to being good most just leaky. it turned out great nice sharp picture ,sound nice and clear ,after going through the tuner its like a new set now.

i found the culprit, it was a resistor went bad, and it took out the cap,
heres pictures before it blew (it was just restored, i didnt get to align it yet)
It has a kind of weak picture tube

I think it's more likely the cap went bad and took out the resistor.

I think it's more likely the cap went bad and took out the resistor.



I'm with Bob on that...

Saw a real good confetti storm once in a previous job. They were working on MRI gradient amplifiers (essentially a big honkin audio amp 300V @ 100A) and had a good sized capacitor bank (probably a dozen large caps) sitting on the bench with an insulator and a DVM sitting on top of it. The power source was a 600V/100A supply adjusted to 350V. One day we heard a hissing sound and someone yelled "DUCK". Apparently the power supply lost regulation and put out full voltage whatever that was. Big confetti storm and the DVM (an HP bench job) was thrown through the ceiling.

put the 5u4 back in, broke the socket! problem solved, turned the set on bbbbbbbbbbbbbbbbzzzzzzz


Ya know, it's a good thing you work on B&W sets. I shudder to think how many rare color chassis you might have destroyed if you were a color fan, please learn as much as you can on these sets first.

Ya know, it's a good thing you work on B&W sets. I shudder to think how many rare color chassis you might have destroyed if you were a color fan, please learn as much as you can on these sets first.

i already know about these sets, and i do have colors too.
when i restored it, this cap tested good, it just failed.
its not anybody fault.

How did you test it ?

How did you test it ?

I used a scope

How do you check a capacitor with a scope ? You need to apply the working voltage (typically 300-450 volts) and check the leakage current. It's also a good idea to check the capacity after the leakage to make sure it's not open.

A vintage tester like this doesn't cost much.
http://farm5.staticflickr.com/4143/4917572714_bb085efbaa_z.jpg (http://www.flickr.com/photos/70039806@N00/4917572714/)

I don't have the fancy machine, so when I need to test here's what I do.

I have a chassis which only contains a transformer and a 5U4 rectifier tube, whose output goes through a small value resistor. With the chassis on a variac, I connect a test cap to the output side of the resistor and ground. Each time you increase input voltage to the chassis with the variac, you will notice that the reading on a meter placed across the resistor increases slightly than settles down as the cap charges. If you have a bad one, the reading will go up and up and the resistor will get very hot. Very old caps sometimes take a very long time to reform, some can't be saved at all. I've found that it's not the initial charge that is the deciding factor in a cap surviving at all, rather it's ability to stay formed is what counts.

For example, say you get an old cap reformed. Leave it on a shelf discharged for a week, then repeat the same test. Chances are you will have to reform it again, because it's simply too old to work anymore. Dry electrolyte, corroded plates, ect. You will notice that you have to wait and wait for the meter reading to come down before you can apply more power, and the cap should be tossed.

Some caps hold form just fine, especially if they come from the NOS pile. I've had pretty good luck charging caps this way, last set I did was a pair of old Sprague cans. Rated voltage on them was 450, and they were 250uf per section. It took me about a half hour, but they formed great and even held up at 525 volts with minimal leakage. Same result a week later, that's how you know you got a winnah.


You could also build the circuit from this site, looks like something we should all have on our benches.

http://www.electrojumble.org/reforming.htm