while we are on 70's SS gear. With some of these sets containing dozens and dozens of little caps, is it even
profitable to repair them? What kind of estimate do you give?
It would have to be a high end receiver to warrant such a shop bill, which makes them all the harder to do, since they
are giant in size, complicated and weigh a good amount.
Just ordering all the caps, diodes and resistors would create a pretty good wait time for parts

All very true.

In my case. I love my preamp. I love the variable loudness contour. It is an extremely useful feature. The phono section is also very flexible, a rarity these days.

It will be worth it to me - but then I'm the one doing the work.

Some people should not be allowed near a soldering iron....

This is one of those odd subjects where common sense is often overlooked.
Capacitors can fail for a wide variety of reasons. Not just because they
are old or new or round or blue. There are catagories of caps that
have a reputation for failing. These include 'black beauty' and other
paper caps with molded plastic bodies that crack. Also wet slug tantalums
have a bad habit of shorting and even exploding. Most people that have
experienced these failure will replace them in equipment they want
to be reliable. Regardless of manufacturer.

Electrolytics of all ages can dry out and loose capacitance. This applies
to new equipment and old. A big factor here is how hot the environment
they operate in is. And of course poor designs where caps are being
operated too close to their ratings cause failures. LCD TVs are
a prime example.

How people approach restoration and repair depends a lot on
their experience. What they do is up to them and some lessons
are learned the hard way!
Steve

In the early 2000s, there were a number of low budget capacitors made using bootlegged manufacturing processes. The electrolyte formulation in these capacitors was missing a preservative, and almost all of these capacitors failed catastrophically within 3-5 years of use. This was called the "capacitor plague."

However, even reputable capacitors can fail unexpectedly. I have an early 1990s vintage Sony CDP-291 CD player in which the capacitor that filters the -40 volt rail for the vacuum fluorescent display shorted out, exploded, and cremated some of the rectifier diodes. Sony did not use cheap capacitors, nor did they put them in a hot environment. Unfortunately, the Sony's power supply design was such that the shorted capacitor placed excessive voltage on the filters for the 8 volt rail, so those capacitors eventually ruptured. I do blame Sony for its weird power supply that included neither a fuse nor a switch on the primary of the power transformer.

I'm not arguing with any of the practical reasons to replace caps, but I wonder if anyone in this hobby cares about preserving as many of the original parts as possible? For me, the hobby has historical and aesthetic aspects as well as technical ones. I see a vintage radio or TV as an artifact from the past and I want to preserve, where I can, the look, feel, smell, construction and wiring techniques, etc. of the era. I like to look at the underside of the chassis and think about the workers who put those parts in and soldered the connections one day way back in the 20th century...it's like a time capsule!
Of course it's easier to pursue this policy with some kinds of equipment than others...I'm more inclined to worry about filter caps in a set with a power transformer or field coil that's hard to replace, and I'm more concerned about out-of-spec caps in a piece of precision equipment. I'm pretty lenient with AA5's or AA6's because they have such non-critical circuits and because, let's face it, most of the paper and electrolytic caps were out of spec (by today's standards) by the time the set was 6 months old...but they were working just fine by the standards of the day.
I repair or restore this stuff for myself, so I can deal with failures when they occur. If I were restoring for the general public, I'd make very different decisions. But I have to say, I've been pleasantly surprised at how infrequently original caps have failed on me. I wonder if it has to do with the fact that I always try to get restorable sets that have been kept in a decent environment, not in basements or barns. Moisture and extremes of heat and cold probably contribute to cap failure as much as the mere passage of time.

Doug E.

From my experience (considerable) the newer the capacitors in CONSUMER gear (70s 80s 90s vintage) the poorer quality they were. And by extension, the shorter their life span. This does not necessarily hold for commercial or professional equipment, where they generally used the highest quality parts available. (no flames and arrows please, I said "generally" ).

I suppose there is always going to be a tradeoff between changing 100 little 'lytics in some "newer" equipment, vs just repairing the problem currently at hand. It depends on what your long term goals are. As far as OLDER stuff, vintage 30's through 60's .. I wouldn't even consider NOT replacing capacitors. Life's too short.

I have restored no end of flat screen tv's in the 30-50" range where a large electrolytic in the power supply was the only problem While I'm at it, the rest of them get replaced. Switching caps in particular, in consumer gear, are selected by the manufacturer to be "just good enough" (cheap, in other words) and do not stand the test of time.

but that's just me

I think this is a good time to distinguish between:

1) wholesale replacement old capacitors as a safety precaution (and proper restoration) in a working set and:
2) wholesale replacement of capacitors before ever turning a set on.

There are some who suggest that every capacitor in a set should always be replaced, in every situation, prior to plugging the set in. This is what I disagree with.

There are those (such as myself) who suggest that as a normal course of troubleshooting a set, "prior to restoration", wholesale replacement is not only not necessary, but may actually hinder the process by not establishing whether the set even works before starting to replace parts.

As I have said before .... wholesale replacement is a choice, and my choice is to test and repair first, then only restore (including wholesale replacement of capacitors) those sets that I plan to play for any length of time.

YMMV

John

Same here, and They want me to replace all the caps in the 70's gear.

+11.5 TO THAT!! But this is where the professional diverges from the newer hobbiest, or the completely untrained. Wholescale capacitor replacement, if done wrong, in a hurry, or without proper experience, can and does introduce an entirely new set of "things that can be wrong with the unit".

I'll replace any obviously bad caps such as leaking electrolytics, do a quick resistance check on any suspicious looking wax etc caps or perhaps even all of them just with an ohmmeter to rule out direct shorts, and then bring it up on a variac.

THEN. ... replace the caps

What you get all too often is someone relatively inexperienced, or completely inexperienced, replacing capacitors as if their life depended on it. Errors occur in soldering, improper value selection, improper type .. you name it. a million new variables

I find myself in general agreement.

I think with regard to power supply electrolytic capacitors in 30+ year equipment, these should either be tested or replaced prior to power ON if the equipment has been sitting unused for a prolonged period. The risk to expensive parts is just too great to do much less. The use of either a dim bulb or Variac to slowly bring up power might mitigate that risk to a degree.

With regard to wholesale replacing ALL capacitors prior to getting the radio running, this can be a function of whoever is doing the replacing. If someone is real good at being careful to not create new problems in the replacement process it can go fine. If someone might be prone to mis-connecting things it would not be wise. In those cases, by the time they are finished, the radio could almost become unrecoverable. Those who are prone to mis-connecting things seem to be closely related to those who have serious difficulties in reading a schematic.

In cases where someone might make a mistake and has trouble with schematics it seems to be best to restrict replacements to the power supply capacitors prior to turning on the radio. This might be extended to that audio output tone capacitor connected to the plate (trying to protect the audio output transformer).

Then at first power ON you can see if the radio is starting out with problems before you create any new ones (hopefully).

From that point if there is no problem you just continue capacitor by capacitor while checking the radio from time to time for continued operation. If things stop working, you check over the things that were done since the last time it worked. At least the potential errors might be easier to find.

Now, if the radio doesn't operate at first power ON with a safe power supply, then there is a decision to make. Do you try to first find the problem, or just motor on and hope that in the rest of the replacement process you stumble across the problem? My tendency would be to try to find the problem, but others may choose differently.

What is my reasoning with regard to choosing to find the problem? Well, it could turn out that the problem is a deal breaker that renders any further work pointless. This could be something like a bunch of fried coils, open unobtainium transformers, unreversible modifications that don't work, or something else. Of course many of those things could have been caught by simple resistance checks before applying power, but this may also be over the heads of people who have trouble with reading schematics.

The bottom line here is that there is no single perfect answer to the process that fits everyone. Each person ultimately has to figure out a process that works for them. Having said that, I believe anyone attempting to restore/repair a vintage radio should first try to develop a working basic knowledge of how to read a schematic and be able to locate a schematic component within a radio and visa versa. They should also have at least a rudimentary idea of the signal flow through a radio from the Antenna, RF, Mixer, IF, Detector, 1st Audio, Audio Output, to the Speaker and how all of them get their power from the Power Supply.

Not being able to navigate a schematic at least to some extent is like being lost in the middle of a city with a perfectly good map and not being able to understand what the map is telling you.

If you understand a schematic even somewhat, then people can help you when you get lost. Without that you are pretty much on your own.

Curtis Eickerman

You must determine initially if a vintage set will be used or just displayed.

For shelf queens, I normally leave all original parts in place, and disable the power supply.

For a user, safety and reliability trump originality.
I put the replaced parts in a plastic bag.

- Leigh

There are so many capacitors and so much information about them (advertisements in the old magazines, photos, and brochures) that keeping the actual units is pointless. However, the old capacitors and resistors can be placed in a bag inside the radio cabinet.

Imho, keeping as many original parts as possible equates to keeping the old washers and packing from a faucet rebuild, or the old bearings from your auto alternator. New parts make things work.

For those to whom absolute aesthetics are important, restuffing old capacitor shells would be the way to go I think. Although when an original fails later, you won't know which are new and which are replaced.

Personal preference ... mine .. is to replace the old worn out parts with bright shiny new ones that work. If done neatly and professionally, I don't see how that detracts from the unit.

It detracts from the appearance for those who are going to pull the radio out of its case and turn it upside down.... uh..... yeah... no one but another restorer

Curtis Eickerman

I'm listening right now to my favorite AM station in the Los Angeles area, KSUR 1260, on my DeWald Model K-702-B transistor radio, which is all original, built in the 1950s. I wouldn't use the DeWalt K-702-B radio every day if it was a tube radio as I would be concerned of a component failing, but I didn't pay much for the transistor radio and it uses a 9 volt battery.

Replacing capacitors is not an obsession , it's a habit, a belief, a benchmark, the best practice. For sets you'd like to power up at least.
If you have a cap or another component leaking oil or PCP's, I'd replace it regardless

A big consideration is that electronics has changed.

In the tube era, the average consumer device had a few electrolytics, in the power supply, to bypass the cathode in an audio stage and sometimes to couple audio stages. If you heard hum from the speaker, change the electrolytic. If audio gain was down, change the bypass capacitor.

Electronics advanced pretty fast, but the tube era is now decades in the past. Wonders like the SP-600 or the Collins R390 date from the fifties, receivers incredibly advanced from the coherer receivers of the early days of receivers, but individual components were still primitive. Nobody would use paper capacitors once ceramic bypass capacitors were available, even apart from going bad, paper capacitors were bulky, and because of the way they were made, imperfect at radio frequencies. But at the time, such receivers used "the best" paper capacitors available.

Things changed drastically when transistors came along. The average consumer equipment suddenly had a lot of electrolytics. Tubes were high impedance, hence few high value capacitors. Transistors were low impedance, hence needing high value capacitors for the same types of circuits. Electrolytics weren't specified, but they were the only way to get the higher values in a reasonable size. Because of the way electrolytics are made, they can "dry up", and with so many in a circuit, the "bad one" is less immediately obvious. I remember even in 1971, "motorboating" wasn't uncommon, a result of a low value or bad electrolytic.

Technology also got better at making smaller capacitors. I have a "computer grade" 10,000uF 15V electrolytic I hot about 1973. The size of a Coke can, with screw terminals. That was high capacitance at the time, yet barely usable because the voltage was barely enough. They have gotten much smaller, with larger capacitance and voltage, in the decades since.

For a long time those electrolytics only had to deal with 60Hz from the line, or audio frequencies. But as switching supplies took over, they were expected to handle much higher frequencies. For a long time those were treated more as black boxes, much easier to change electrolytics than try to understand what was wrong. As digital electronics advanced, electrolytics were counted on to keep power buses "clean" despite more and more current being drawn, and at much higher switching frequencies. That's harder on the electrolytics and will stress them faster, even assuming the right ones were chosen to begin with.

Tube consumer electronics (not that there was much of it) was relatively easy to repair, things were accessible. But other equipment was better built, which meant endless effort to get to some stages, so why not change the capacitors when in there? Recent electronics is incredibly compact, it was easy to fix that LCD monitor I found because the power supply was mall and easy to access, though I changed the output filter capacitors and it works fine. It had been resetting, and I would have expected the problem elsewhere.

So over time, the "shotgun" replacement of capacitors has continued, but for different reasons and different capacitors are changed.

Michael

If the radio theory isn't there with a individual some will shotgun the chassis with caps and hope for the best before reading or watching You Tube for all the radio theory they can acquire before diving into the repair world. The fast pace, or getter done times of today. JMO

I seem to remember an over zealous and very excited newbie working on a 10 tube Zenith chassis. He was so new and excited to get going that he cut out ALL the wax caps without thinking. He was left staring at 2 piles of caps, one old and one new.


After that I learned how to read schematics, and do caps one at a time .

The term "shotgunning" is derogatory and totally unjustified.

It's usually used by those with minimal knowledge to describe folks with more knowledge.

I'll put my electronic credentials up against anybody on this board.
I ALWAYS replace vintage capacitor types that have poor reliability.

It's called "learning from experience" and "taking pride in one's work".
I expect my repairs to last longer than I will.

- Leigh