Paper & Oil Capacitors /Pro's / Con

[plexi50]

I have picked up 3 Wurlitzer organs in the past 3 weeks. Mid to late 60's. There are alot of oil and paper caps in these things. I was wondering if the caps could still be good after all these years. I know caps all dry out at some point in time. I have no experience with using paper & oil caps or the pro's and con's of there life span

What is your experience with old paper & oil caps?

[thermion]

They are like the red-headed girl: when they are good they're great and when they're bad they're TERRIBLE! Vintage PIOs follow this rule just as new ones do. I have vintage sprague vitamin Qs that are awesome beyond comparison. I have new sequa PIOs that are total trash. I have new jensen/audio note PIOs that are REALLY good, approaching vitamin q.
My 63 wurlitzer organ had pretty middle-of-the-road quality parts in it if I remember right - not junk but not mil-spec either.
Pull em out, test em for leakage and value. If they pass give them a shot.

[jerrydyer]

are the vitamin q worth the dough? thanks

[Geezer]

vitamin q worth the dough?

Good gracious, $13+ a pop?!! 

I'll stick with my $0.25 polyesters!

[plexi50]

There are so many of them in the (2) organs i parted out that it will take a week of desoldering to get them all out

[Vair_dude]

I've got a model 4075. Something smoked in the power supply. Should be right around the same era. I thought about either fixing it or using it for firewood. I'm leaning towards firewood.

[plexi50]

I took one of them and made a cabinet out of the wood. The wood is just to pretty to throw away to me /

[pullshocks]

How do you test for leakage?

[sluckey]

How do you test for leakage?

I just use an analog ohmmeter set on highest scale. You should see a kick (higher value caps produce a stronger kick) when you connect the probes but the resistance should settle down to read infinity. Any resistance reading indicates leakage. Don't touch the cap leads while doing this or your body resistance will probably interfere.

[plexi50]

I have used an Analog for testing electrolytics but does this work for tone caps as well?

[HotBluePlates]

When I get back home, I'm gonna do a little testing with some known good, new caps (Mallory's, Solen, etc) and a few questionable caps (Sprague bumblebee and black beauty, pulled from and replaced in old equipment).

Because I have a dc power supply and a dc microammeter, I plan on measuring the leakage current directly. I've got notes somewhere of typical leakage for good caps of various types, but the idea is to reference the new caps as a benchmark of what's acceptable (and that varies a bit with dielectris, and especially with e-lytics).

[sluckey]

I expect all electrolytics to have leakage, but I expect all my small caps to have zero leakage (infinite resistance on an ohmmeter). A small cap used in a circuit that has no dc voltage on it such as many tonestacks, may go unnoticed forever but that same cap used to couple a plate to a grid would have much more noticable symptoms. I just don't want to tolerate any leakage in small caps. Here again, I'm talking about leakage that shows up as a measurable resistance on an ohmmeter.

[SoundmasterG]

The best way to check leakage is in circuit. Unsolder and lift the lower voltage end of the cap, and stick your meter between the open end of the cap and ground. Turn the amp on and you will get a surge and then the voltage will somewhat stabilize. What it settles on is your leakage. You shoul dbe checking on DC btw. The reason this is better than checking at low voltages is because the cap should be checked close to it's rated voltage to be accurate. You should have less than .03v for a 400v cap...anything more than that and it will throw the bias off of the stage following it.

Another way to check caps for leakage, and out of circuit, is to get a Sprague Tel-Ohmike or other vintage cap checker. These are great and test all sorts of caps up to 600v if needed. You can also use them to re-form caps if you need to. You can find them on ebay.

Greg

[HotBluePlates]

Unsolder and lift the lower voltage end of the cap, and stick your meter between the open end of the cap and ground. Turn the amp on and you will get a surge and then the voltage will somewhat stabilize. What it settles on is your leakage.

Believe it or not, I tried that and measured 40-70vdc on a number of old coupling caps!!

So I got to thinking about it, and looking at the TelOhMike and other testers. I noticed that everyone is attaching the cap to a dc supply and then doing some form of measurement.

If a cap leaks, then it is by nature a leakage current... the problem is that even a little current across a 1M resistor can result in significant voltage when you're looking at small-signal tube biasing. But what I got to thinking is that if I measured voltage while lifting the end of a cap, then the measured voltage is going to be the leakage current * the input resistance of the meter. Assuming my meter was 10M input resistance, and I measured 40v, then that's only 4uA of leakage current.

I could buy a cap tester, but I've got too many other items of test gear, and that includes some regulated dc supplies that will make 300-400v and a HP Microvolt-ammeter, which can measure down to 1pA full scale. My thinking is that the voltage measurement could be slightly misleading depending on how the test is arranged, but a current measurement will give consistent and relatable results. Icare about being able to make comparisons between caps because I have a bunch of old test gear and some old audio gear to refurbish and verify (some full of Sprague bumblebees, which are known to leak).

[bigdaddy]

I took as many caps as I could find, all different types. Some a little expensive, some old (Sprague)and some new, also the SOZO older not the handmade more expensive ones. PIO, Mallory, orange drops, Auricaps, everything....and anything. I had maybe 15 caps or more all on a terminal strip. They all measured close to .022. I used a BF champ clone and used them for the coupling cap before the 6V6. I had a wire with a clip so I could go back and forth between them. I did it a few times over a few days because as I learned from recording after an hour your ears go dead and everything sounds the same.

The next to the best sounding ones were the orange drops both 714 and 715 and the Mallory's. The Mallory's were a little dirty with a little trash in the sound but smooth and toneful. The orange drops were a little harsh but with a bit more highs. So if you were to do a complete cap job I would and did mix them in the past. I had amps filled with all Orange drops and they were not the warmest amps, kind of a bit louder and harsh, to use a few Mallory's in there would smooth it out. I also would use silver mica coupling caps before the PI in some amps that sounded better with 500PF over the bigger .001 caps some Fenders called for.

And the winner was, the Jupiter caps. I made sure I had used them a while before I tried them. They had everything that was good about the Mallory and Orange drops and none of the bad. I later tired the new handmade SOZO cap in both yellow and blue and they too sounded wonderful and similar to the Jupiters but it really depended on the amp. I really feel if you want that Marshall or Brit sound the SOZOs are the way to go and if you want an American Fender type sound Jupiter or the blue SOZOs are the way to go.

I would really like to do it again but it was time consuming, slightly expensive and without help a real pain. But if I do I will wrap each one in something so I cannot tell which are which. I do trust my ears enough to not let my eyes fool me. Having had a sound reinforcement company I had to not let that happen and trust my ears completely. But I still would have liked to have help and did it right. After building a lot of amps by now I think the most important cap for tone is the coupling caps. And value even more than the type. But an amp is the total of each part, in some amps a ceramic disc over a preferred silver mica might do enough to add some of that so called mojo. In the end it's all about what the individual likes and how well he or she can play their instrument.

[bigdaddy]

And I forgot to say the PIO were one of the worst sounding. I had one from Russia and one that was more expensive. I just don't have it all written down anymore. They sounded horrible. I was so disappointed because they were so expensive.

Although I did hear an 18 watt clone with an EF86 and what looked like PIO and ceramic discs. This amp was on a clip on some website. I lost the web page, it had been on the internet for a few years but I will never forget the tone of that amp and it was that amp that made me do the test. It was also the amp that got me interested in trying Pentodes along and instead of the typical triode.

So who knows maybe EF86 tubes sound better with PIO caps????????????????? Oh well that's a whole other test.