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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Feb Wed 14, 2018 5:37 pm 
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We use my 1984 Yamaha pre-amplifier and amplifier most every day. Perhaps I should at least check the electrolytic capacitors. Would you replace them?

Leigh wrote:
Of course, we had no "lowest bidder" requirement. We were trying to do real stuff. - Leigh
FYI, low bid is not always bad. One of our Caltrans contract managers cried when the contract with my environmental consulting company was over, as they had had so many awful consultants win other bids. My company has won many government contracts where the award was based only on price. We do not have the high overhead of larger companies, so are able to provide superior quality AND superior value. One of the biggest mistakes larger companies often make is hiring numerous low-paid trainees or junior staff, forgetting that senior experienced people are not only more effective, but more efficient.

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Feb Wed 14, 2018 6:05 pm 
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FStephenMasek wrote:
We use my 1984 Yamaha pre-amplifier and amplifier most every day. Perhaps I should at least check the electrolytic capacitors. Would you replace them?


The best way would be to test them, although for the electrolytic caps used as coupling caps you can get the schematic and measure the voltages on either side of the caps and that may give you an indication if a cap is failing short. A coupling cap that is failing open will manifest itself as a drop in audio level or a reduction in bass. A filter cap that is failing open will result in either hum, low frequency oscillation if (if the cap is bad enough) or both.

Then again if the preamp works with no issues whatsoever it may be best to leave it alone.


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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Feb Wed 14, 2018 7:05 pm 
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I recently re-read the section in Alan Douglas' book about checking capacitor ESR ... and his general thoughts on the whole subject. I share most of those thoughts, which summed up and simplified boil down to ... replace'em all !!! ............

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 3:45 pm 
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Barry H Bennett wrote:
I recently re-read the section in Alan Douglas' book about checking capacitor ESR ... and his general thoughts on the whole subject. I share most of those thoughts, which summed up and simplified boil down to ... replace'em all !!! ............


+1

But in reading over the advice given out by experienced ARF people to newbies it seems like newbies are being led to believe that changing capacitors will fix everything. Advice to change caps is just part of good vintage equipment maintenance but not a silver bullet that will fix everything, And that is what is often being dispensed here. It seems that every follow-up posting for a newbie directs them to change the caps first or worse, only to change caps and this is not very thorough troubleshooting technique. Yes, yes, yes, it is important to change capacitors but the implication predominantly seems to be that capacitor changing is the cause for every problem. What happened to checking inputs and outputs, tube voltage and resistance checks, signal flow etc?


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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 3:59 pm 
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As a relative newbie and at the risk of raising the ire of many on this forum, I don't automatically replace capacitors when faced with a nonworking radio, and here's why: I'm trying to learn about tube radio circuits and troubleshooting, and if I replace all the capacitors and then turn on the radio and it works fine, what have I learned? In other words, I want to hear what a bad filter cap sounds like, the symptoms of leaky coupling caps, unwanted oscillation caused by bad caps, etc.

I readily admit that if one is a master at this craft, or is restoring radios as a business where time = money, replacing caps a priori makes sense. However, for people like me at the very onset of learning about old radios, replacing capacitors one by one and watching the change in radio performance, is invaluable. Best done with common radios without unobtanium transformers of course!

Bryan


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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 4:13 pm 
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Quote:
Best done with common radios without unobtanium transformers of course!

....And there you have it. Perhaps you might better replace caps that can FRY things you cannot replace, or at least check them with a properly maintained capacitor analyzer, before powering up. While it's probably not a big deal if a shorted or leaky cap causes a tube plate to glow red, it's a different story entirely if a bad cap cooks an output transformer or a power transformer.

I think that's at the root of why most advice on here says to replace first, ask questions later. That said, if you can either replace or test those that can lead to these tragic results, you can then spend endless hours troubleshooting your way through the rest of the circuitry. It is, indeed, a good way to learn. I'd consider it frustrating as well, since we all know that the vast majority of 50+ year old capacitors have either gone leaky, or worse, or will.

The filp side is ... replacing a cap with the wrong one, or a miswire, or other mishap, can lead to it's own set of headaches, so there is a case to be made either way. You'll have to decide, based on your own experience and expertise. Likely some combination of all the advice given would be a good starting point for you.

that's just my take on it... others will vary.

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 4:44 pm 
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Paper caps and electrolytic caps indeed should be replaced first especially if the person is inexperienced.

Now sometimes I will power up a device using a variac and connect my dmm to the last filter cap in the power supply.

As I turn up the voltage I watch for dc voltage on the cap at which point I may leave it there a few minutes then I'll start increasing the voltage more. If at any point the voltage on the last filter cap does not increase and is a good bit lower than what it probably should be I do no further tests.

Now if I get to full line voltage and all seems ok with B+ I proceed to test the device's operation.

I normally only do that so I can see the device work as I know I'm going to replace the resistors and caps anyways.


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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 4:47 pm 
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Sparksalot wrote:
But in reading over the advice given out by experienced ARF people to newbies it seems like newbies are being led to believe that changing capacitors will fix everything.

I've never seen such a suggestion, and certainly have not stated such.

The reason for simply changing all the old electrolytics and waxed paper caps is to increase the chances that you can safely apply power to the set for further evaluation.

Vintage caps have usually failed already. Those that are still functional will likely fail soon.
Eliminating those problem areas before applying power reduces the chance of damage.

- Leigh

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 5:13 pm 
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FStephenMasek wrote:
One of the biggest mistakes larger companies often make is hiring numerous low-paid trainees or junior staff, forgetting that senior experienced people are not only more effective, but more efficient.


That's so true, win a big contract, then start hiring and training, put the new inexperienced techs by themselves on 2nd and 3rd shift, give them
minimal support, put the pressure on and watch your new techs quit or fail, then put your big contract at risk, who is that? Canon USA among others.
That is the STUPIDEST management style in action, let your senior techs make their own schedule, no weekends, no shifts, then watch your important customers
fail because the real knowledge sits at home with their phone off.
Customers aren't paying for lack of knowledge or experience, nor should they pay for you to run "On the job training" or discounted service.
But 1st line managers are usually without fortitude or even enough guts to run their part of the business

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 5:49 pm 
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Sparksalot wrote:
Barry H Bennett wrote:
I recently re-read the section in Alan Douglas' book about checking capacitor ESR ... and his general thoughts on the whole subject. I share most of those thoughts, which summed up and simplified boil down to ... replace'em all !!! ............


+1

But in reading over the advice given out by experienced ARF people to newbies it seems like newbies are being led to believe that changing capacitors will fix everything. Advice to change caps is just part of good vintage equipment maintenance but not a silver bullet that will fix everything, And that is what is often being dispensed here. It seems that every follow-up posting for a newbie directs them to change the caps first or worse, only to change caps and this is not very thorough troubleshooting technique. Yes, yes, yes, it is important to change capacitors but the implication predominantly seems to be that capacitor changing is the cause for every problem. What happened to checking inputs and outputs, tube voltage and resistance checks, signal flow etc?

SOP is to change capacitors first, both Electrolytics and wax. Resistors can also be measured for tolerance, and replaced if needed. I've found that usually few if any need that, but it's always good to check.

Personally I've always advised that after doing that, assuming adequate operation of the set afterwards, to do an IF and RF alignment to peak the performance. In most cases, these three operations will restore the circuit to near factory performance, maybe better, and it's sound advice for both tube and solid state radios.

Now there's always a chance that a tube also needs replacement, an audio transformer has an open primary, the tuning capacitor is noisy or doesn't allow reception over a certain portion of the band, or a speaker produces sound incorrectly, but these are almost the exceptions, and generally can be easily handled, esp by asking here on the board.

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 6:09 pm 
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I finally stopped checking resistors, except out of curiosity. Somebody here mentioned that the modern ones are more stable, something which matters more in the RF sections. Now, I just replace all of them while I'm busy replacing capacitors, especially since there is usually a need to de-solder at least one end of each to replace a capacitor or wire.

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 6:27 pm 
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There was an old saying that was taught to me years ago that is true.

“Why is there never enough time to do it right the first time, but plenty enough time to go back and get it right the second time”

I want to do the best job possible so I don’t have to revisit it later. Where I work, I would not want to see our internal customers calling us back about the same problem because we skipped a step. Makes us look bad, and it causes the end user to loose faith in our abilities.

For me it’s standard practice to replace all capacitors and resistors in an old radio. Has never failed me yet, and I won’t change my ways. When a friend of mine said he bought a bunch of old wet electrolytics to see if they could be reformed, I nearly doubled over. He was serious. :shock:

In the end, to each his own. It’s your life and your opinion and I won’t force mine.

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 7:37 pm 
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My procedure is (puts on my asbestos suit)

Replace electrolytics… Those are guaranteed to be bad.

Replace paper caps with B+ on them especially after a sensitive item such as a shadowmeter or other coil winding.

Then power it up on a Variac monitoring current draw, and go from there. Check operation and replace as needed.

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 7:45 pm 
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azenithnut wrote:
My procedure is (puts on my asbestos suit)

Replace electrolytics… Those are guaranteed to be bad.

Replace paper caps with B+ on them especially after a sensitive item such as a shadowmeter or other coil winding.

Then power it up on a Variac monitoring current draw, and go from there. Check operation and replace as needed.

-Steve


That works very well, particularly for those of us with enough experience to quickly sense that something else is wrong. I'm good with changing the electrolytics and a few critical coupling caps to output tubes or bypasses from plate to ground, and cutting out any line bypass or across the line caps, then testing operation. But quite often that test will show something else that needed immediate attention.

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 7:47 pm 
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My only point is that, at this stage of my learning how tube radios circuits work and the appropriate diagnosis of such, I learn more from a non-functioning radio than I do from a perfectly functioning one. I'm not fixing radios for customers, or for sale, but rather simply to learn about the circuits and the function of each of the components. Could mistakes happen? Yes, of course, and I do take appropriate care to make a few tests before powering it up, and bring up the radio on a Variac and monitor the B+ while doing so. If anything seems amiss, I shut it down immediately until I can study it further.

As an experimentalist by trade (chemist), I always felt that I learned more from experiments that didn't work than from experiments that worked perfectly the first time. I fully admit that once I have the experience under my belt that many on this forum have, I won't waste time fooling around with capacitors that almost certainly are bad (or soon will be).

Bryan


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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 7:51 pm 
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You can definitely get an education on how circuits perform with bad capacitors in place by doing one at a time. The only issue is not being able to prevent collateral damage should one decide to catastrophically fail. While that won't happen every time, once could be too often if the part it takes with it is unobtainable or horrifically expensive.

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 7:55 pm 
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Dennis, I fully agree. The radios I "experiment" on are typically rescued from the dumpster with almost zero retail value. One day that may change, at which point I'll approach things differently.

Bryan


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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 8:37 pm 
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Old Rad Lab wrote:
As an experimentalist by trade (chemist), I always felt that I learned more from experiments that didn't work than from experiments that worked perfectly the first time.
Hi Bryan,

That's certainly true in most fields, not just electronics (or chemistry).

There are many commonalities in experimental techniques across disciplines. You appear to be far more advanced in that general area than the newbies we commonly encounter.

One of the problems with internet fora is that they are mechanisms for strangers to help strangers. We have no way of knowing the skill level of the person posing the question. So our responses are tailored to the "average" skill level of our new members.

That is not meant to insult nor exclude anyone. All are welcome, and we try to help everyone.

Our general guidelines are biased in the direction of safety. I would feel very bad if someone followed our suggestions only to have the radio blow up in his face.

- Leigh

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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 10:17 pm 
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I replace the caps because over time they will fail before tubes and resisters. I would like my radios to out live me and as long as they work, maybe they won't be thrown away. I just finished up the chassis of a Hallicrafter Portable a lady friend found for me to fix. 8 Blackberry's and 1 red one. I test them as they come out because it's fun using my R-C tester. ( simple things make a simple mind happy). EVERYONE was bad and I mean BAD. So far off that I questioned my tester and my settings. The best one was .01 and tested at .5. All the others were giving wacky readings. I have noticed that radios from the late 50's and early 60's have caps that are pretty close to specs.

Think I'll continue replacing caps.
Freeman.


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 Post subject: Re: Public obsession with replacing capacitors
PostPosted: Mar Sun 25, 2018 11:03 pm 
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Does everyone who is preaching wholesale cap replacement before ever firing up a radio .... also change them in:

radios that are not going to be used regularly?
radios that are old enough to be unique and should go to a museum?
radios that might already have something wrong with them that might make them not economical to fix?
radios that you have two of and plan to make one from .... but ya' gotta' see which one is the donor and which one to fix?

Or .... do you sometimes turn on a set that isn't (horrors!) shotgunned?

Despite trying to scare newbies with stories of failed caps taking out transformers etc .... how many of you have actually seen a radio fail expensively during a quick power up test run? ..... sure it happens, but .... probably to very few of you and of those few it was probably a microscopically small percentage of the sets you've powered up.

Instead of preaching gloom, doom and failure, why not teach how to do a safe power up and trouble shoot? Why not use the tools of your trade?

I am in favour of the "safe startup", then troubleshoot to determine whether or not to repair and/or restore.


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