Why should someone replace ALL the capacitors on old Tube equipment?

If you remove every paper and foil capacitor from an old tube anything and check them on a quality checker, you'll find most if not all showing some s ort of defect. They may read OK value wise, but run a few hundred volts th rough them and you'll find most have a lot of internal leakage. The fact i s that moisture does eventually penetrate the capacitors and causes problem s.

I've heard that old Radiolas use large banks of paper and foil capacitors i nstead of electrolytics and most do just fine with their original caps. Su pposedly it's because of the particularly fine rice paper imported from Jap an used to construct these capacitors during the 1920s. These rice paper c aps might escape degradation over the decades. Perhaps those who've restore d a bunch of these can comment if they actually did dynamic testing of the capacitors.

Most "old" radios are from 1930-1960. That makes them 87-57 years old.

Manufacturing has changed a lot.

I change all the caps simply because I don't waste my time "troubleshooting" bad caps. Bad caps can cause collateral damage. Why risk it for the cost (low) of replacement parts?

Old electrolytic filter caps dry out. It's a fools game to waste time trying to reform them. Paper dielectric capacitor absorb moisture and that combines with the acids in the paper and cause them to fail.

For the most part, mica, silver dipped mica and ceramic capacitors are very reliable. The band ones, you can find AFTER you've replaced the usual suspects and can actually trouble shoot the radio rather than running around in circles chasing known bad parts.

Yes, I've had to replace the occasional vacuum tube, or found an open coil, but for the most part 99% of the radios I've worked on, worked to a fashion by just replacing known bad parts. I.e. Paper and electrolytic capacitors.

I'm 66 years old. According to my doctor, I dont have any bad capacitors, (just arthritis). :)

Seriously, I wonder what the life expectancy is for the new caps (meaning the replacements for the wax coated paper caps. ???)

And what are these newer ones made from?

I know the mica and ceramic caps are reliable and last almost forever.

A for electrolytic caps, it seems that the newer ones have a much shorter life than the old ones did. You'd think that it would be the other way around with modern technology, but today the name of the game to to make stuff as cheaply as possible, for profit, not long life. After all, today's electronics, cars, even homes are disposible. That's why those old radios still work after 60 or 80 years, while most stuff made today is in a landfill in less than 10 years.

One other thing that most people dont know, is that if we have a nuclear blast, all of the semiconductors will cease to work. That means all modern electronics, radios, tvs, cpmputers, cars, and darn near everything around us, will stop working. The only stuff that will still work are tube based electronics and vehicles made which still have ignition points in their distributors.

Most likely WE wont survive either, but if we do, all we will have is the old stuff from the 1960s and earlier, to rely on. The internet will be gone, since it's all run with silicon. Most radio transmissions will also be gone, except those still powered with tubes. This day is coming soon, and we will be tossed back into the early 1900s. Thats why we need to keep this old technology alive. The gear we relied on during WW2 is the gear we will rely on once again during the upcoming WW3.

Actually, the electrolytic capacitors are more likely to be good than the paper capacitors. Almost all of the paper capacitors I have from the "old days" are bad, even if they were never used while a small number of the electrolytics are still functional.

The paper capacitors were made of sheets of foil separated by paper, "sealed" in wax. Unfortunately, wax isn't a very good seal; moisture can penetrate it. These capacitors were a know failure point 10 years after a set was made. There just wasn't anything better to replace them with (at a reasonable price). Modern capacitors are made from plastic film that is much less affected by moisture and is a better insulator in the first place.

The old electrolytic capacitors you are talking about don't sound like the oil filled variety. Indeed, if they are electrolytic, they aren't oil filled. Oil filled capacitors aren't polarized and many of them are good today. They were the high quality capacitors used in military and premium industrial equipment; you seldom find them in consumer gear unless someone has repaired it with surplus parts. The capacitors you talk about are more likely wet electrolytics. They aren't filled with oil but with an acid. They are indeed all bad; don't power a set that has them. Sometimes they leak if you turn them upside down (the vent hole you mentioned). And be careful not to puncture them while you are removing them. If there is still any acid inside, it will corrode any metal it gets on.

You can still get high quality electrolytic capacitors from authorized distributors like Mouser or Digi-Key. No-name ones from Amazon or Ebay are likely to be junk. Name brand ones from these latter sources may be counterfeit.

While tube electronics may survive a nuclear war, it is irrelevant. There won't be any electricity to run them. The power plants are controlled by computers. Likewise, having your own generator won't help either. Many of the new ones are also semiconductor based, and you won't be able to get gas to run them since the pumps at the gas station are run by electricity which won't be available. Solar cells are also semiconductors and the inverters used with them also use semiconductors. So, if there is a WW3, don't count on ANYTHING electrical working.

I'm 69 years old. My body mechanic says I have pump and inside plumbing problems. Perhaps I should replace him with a plumber?

There are online lifetime calculators for electrolytic and other types of capacitors. For example: (click on Capacitor Life) The major culprit is internal heating from high ripple current resulting the electrolyte leaking or evaporating. Temperature also has a big effect. There are graphs on the capacitor data sheets that approximate the lifetime characteristics.

For electrolytics, try polymer caps:

Not all ceramics are that reliable. MLCC (multi-layer ceramic caps) are rather fragile and microphonic.

Nope. The old ones filtered at 120 Hz. The new caps filter at 100 to

Todays products are intentionally designed to be difficult to repair and to only last as long as the warranty period. With the proper design tools and models, it is possible to predict the life of an electronic (or mechanical) product. Anything that lasts longer than the warranty period is deemed to be "over-designed". It is then redesigned using lower rating or cost components so that everything blows up at the same time. I've seen it happen.

One of the factors that is often overlooked is the tolerance of the circuit to the various types of wear-out mechanism.

If a cathode by-pass capacitor on the sound output valve goes leaky, it would have to leak very badly indeed (and measure only a few hundred ohms) before it upset the operating conditions of the valve. On the other hand, if an inter-stage coupling capacitor begin to leak and puts even a small proportion of the anode voltage of the first valve across the grid leak of the second, it will upset the second valve very badly and may even destroy it.

Electrolytic smoothing capacitors in the HT line will leak even when brand new, but the leakage is usually fairly small once they have settled down. If they later begin to leak badly, this will cause internal heating and damage which may not be obvious - the set will appear to carry on working as normal. Eventually, when the leakage increases even more, something in the power supply will fail due to overloading or the capacitor itself bursts; but until that point, there may be no hint that things are going wrong because the circuit is reasonably tolerant of that sort of leakage.

I have repaired QuadII amplifiers which almost met specification even though the internal voltages were all over the place, most of the capacitors were leaking and some of the resistors had changed value too. The initial design was intended to be tolerant of a wide range of component values (close-tolerance components were very expensive) so it wasn't badly upset by drift due to ageing.

Oliver Wendell Holmes wrote a very funny poem about that, "The Deacon's Masterpiece, Or, The Wonderful One-Hoss Shay".

Here it is, read by Eddie Albert.

Cheers

Phil Hobbs

Perhaps those who've restored a bunch of these can comment if they actuall y did dynamic testing of the capacitors.

I have done a fair number of AK55s and their Radiola and other-brand contem poraries, using potted 1 & 2 uF paper caps. I will typically test them at 5

I have never, repeat, never found a bad potted paper cap in an undamaged de vice. The secret, in my opinion, is that the caps are massive (I have unpot ted a couple for the sake of curiosity from rusted-out hulks), with wide cl earances. The potting tar makes for an excellent seal as well.

Peter Wieck Melrose Park, PA

A wonderful poem and read very well.

Thanks, that was good and quite appropriate.

While attending college, I lived for a time in a large old house aptly named "the fire trap". I could hear termites chewing away in the walls. About 3 years after graduating, I returned to visit the school, and drove by house. It looked much the same as when I lived there. The next day, on my way out of town, I drove by again and found that the house had collapsed in a heap. No wall was left standing. According to the news, it had fallen down by itself and without warning, injuring a few students in the process. It's much like the medieval cathedrals, bridges, and other structures, where the failure of one tiny arch, will cause the entire structure to collapse.

In a previous life, I tried to design a "warranty timer" into a product. Actually, it was suppose to accumulate and display the amount of time that the unit had been powered on to help establish maintenance intervals. In previous products, a mechanical counter-timer was used, but for this version, it was deemed too big and expensive. I found a company that made an electrochemical equivalent. It was housed in a glass cylinder, similar to a common 3AG glass fuse. Inside was some chemical solution. When a few volts of DC was applied, electrolytic action caused one end to slowly turn dark, thus indicating the amount of time that the DC was applied. Sorry, but I couldn't find the vendor or an equivalent online. When the required maintenance was performed, the indicator would be replaced as it could not be reset.

During the design phase, I liked to joke about installing a 2nd timer in the product, which would blow it up after a specified operating life. I even designed a place for it on one of PCB's. I stopped joking after I found that management was taking me seriously and discussing such things was how to handle extended warranties. The device was later removed in a cost reduction exercise, but the component outline remained in the printed manual, resulting in numerous embarrassing questions because someone had labeled the part as a "warranty timer".

Something like a coulometer???

Seeing as you brought up WW3, for those of you that may not know it, a new president singlehandedly advanced the Doomsday Clock by 30 seconds just last week. Heck of a job!

You probably don't know this, but it's not a *real clock*. It's one of th ose cardboard affairs that we used to teach our children how to tell time. Some snowflakes have one that they labelled "Doomsday" on it in crayon and they move the hands one way or the other depending on how *they* feel abou t things.

If there were no Muslims and Communists, this would be a pretty peaceful wo rld actually. And speaking of Communists, it was lovely of the outgoing U. S. president to throw the cold war back decades before he left.

That's a heck of a job!

Lemme See:

Austria in 1936. Chamberlain: Peace in our Time.

And we all know how that turned out.

Crimea in 2016. Ukraine in 2017? It is a shooting war to this day, and Ukraine is losing. tRump: Peace in our time, and let's go to bed.

Expect any different? Only this time with Nukes.

On some great and glorious day the plain folks of the land will reach their heart's desire at last, and the White House will be adorned by a downright moron.

In this world of sin and sorrow there is always something to be thankful for; as for me, I rejoice that I am not a Republican.

H. L. Mencken

Peter Wieck Melrose Park, PA

True. But the reason to replace them ALL is that if you only replace the one(s) causing a problem, another will fail later, then another still later. It is much easier to do them all at once than to have to repair the same unit over and over as they fail one after another. Been there, done that.

Waxed paper capacitors are notorious for moisture absorbtion and becoming leaky.

There are plenty of other types of dry capacitors that don't last forever in the high temperature around tubes.

I've seen loads of ceramic caps fail - but mostly in TV horizontal scan sections where the frequency is over 15kHz and high voltage pulse conditions.

This got worse with ever increasing PC monitor resolutions.

AFAICR; mica caps were pretty reliable - in most of the places I found them, they were used for precision and a specific tempco.

Get off of it. You lost.

I believe in replacing most all the components that are similar when one fails in older equipment. I worked at a large plant and when a 200 HP motor speed control went bad a factory man was called in. He found two power diodes bad. As this was a 3 phase motor and had one more, I asked him to replace it. He told me they were about $ 100 each. I said go ahead. The down time was costing us much more than that an hour,and to get him back in would cost a lot more if the 3 rd one failed, it would be just good insurance. The diode may or may not have been weakened in some way. $ 100 is a small part of over $ 50,000 or more.