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 Post subject: An Indication of a "Reforming Capactior" Questions
PostPosted: Apr Tue 07, 2020 7:54 pm 
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hello all,

once the new room was built last april for my 75 ish radios, all of them in the meantime were in climate controlled storage, all wrapped up, and nicely packed away.

all of the sets have capacitors that were replaced within the last 5-8 years, new stock, nichicons, and panasonics.

many of these sets have not been turned on for no more than 2-4 years tops.

i displayed all my sets last april and since new years, i have been rotating one set out of the room, playing it for about 3 days at 8-10 hours per day.

today, i pulled out my Arvin Lefty 544 and when it was warmed up, it had a very little, but noticeable 120 cycle hum to it. it was nothing major, but with the volume down, it could be heard within 2-3 feet if the volume was at zero, one listened, and there was no other noise in the house.

it was a bit "more hum" than the normal AA5 that only used 2 capacitors in the power supply filtering section.

after the set was on for about 3 hours today, i went to check it, turned the volume down, and the hum is totally gone--well, not totally gone, but it was the normal "hum" for an AA5 with your ear up to the speaker--y'all know what i mean...

so, my question to which i believe i know the answer: the new electrolytics that have not been powered up for 2-4 years have reformed in those 3 hours.

my real question: should those new lytics be replaced or is that normal ? are they fine since they caused hum after not seeing power for a few years ?

my shop is not local to me so i can't / am not going to measure ripple, current, and all that, especially since it most likely would have to sit another 3 years for the caps to deform.

what do you all think about replacing them since they deformed in 2-4 years w/o power ? is what i experienced ok/normal/fine ?

shall they go, shall they stay, or shall i just power things up a few times per year like i now plan to do ?

thanks.

steve

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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: Apr Tue 07, 2020 8:32 pm 
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I don't think new caps would make any difference since their not that old. I would power them twice a year like you said,that would do the most good. I realize that's not easy with that many tube radios. I would only replace them if they still acted up.


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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: Apr Tue 07, 2020 8:47 pm 
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I wonder if this background AC hum could be coming from something other than the electrolytic power supply capacitors?

To the best of my knowledge, "reforming" an electrolytic doesn't change either its uF or its ESR. Reforming mainly reduces the leakage current. If the capacitors in the radio aren't getting "warm to the touch" then they probably don't have much leakage current.

Many older AC powered vintage radios have some type of "hum cancellation" circuitry. I haven't studied the details enough yet to fully understand how "hum cancellation" circuits actually work. But i have heard that the values of several components influence how well the hum gets "canceled.” This includes the tubes and the electrolytic filter capacitors, as well as the values of several resistors.

The good thing for your case is that the hum gradually vanished after the radio operated for a length of time. That leads me to think there isn't a major problem in your radio.

-EB

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Last edited by electricboyo on May Sun 03, 2020 4:34 pm, edited 2 times in total.

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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: Apr Tue 07, 2020 8:58 pm 
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I have a Zenith H845 ch. 8H20 AM/FM large table radio which I restored last summer. It went into my living room and was used every day for several months. It gradually developed an "audible" AC hum which is loud enough to be heard from 3 feet away from the radio when the volume control is at minimum. It isn't getting worse, but it is always heard. The hum loudness is relatively constant: It doesn't get louder or softer after playing the radio for several hours.

I suspect the factory-original can-type electrolytic is beginning to fail. I didn't replace it during restoration because it tested perfect for uF, ESR, and DC leakage at that time.

This radio is on-deck to get back onto my workbench so I can correct its hum problem. This is a great sounding radio so I want to get it back into rotation again soon.

-EB

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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: Apr Tue 07, 2020 9:37 pm 
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i've seen grid/cathode problems in the 1st / 2nd audio cause sets to "hum-up" as it is played, so i don't believe that is it. this did just the opposite.

also, this is the outlet and spot where i have powered about 25 or so since new years, so i don't believe it is an interference anomaly. i would have found that out many a time, if so.

it is the normal "filter capacitor" hum as we all know it, very minor, that gradually disappeared.

steve

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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: Apr Wed 08, 2020 9:44 pm 
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whelp, it did it again today.

electrolytics must go.

steve

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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: Apr Thu 09, 2020 3:54 am 
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I beleive it's got left-hand-itus and is trying to hum Hey Jude in a monotone. Send it to me for analysis. :lol:


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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: Apr Thu 09, 2020 4:29 am 
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it would be cheaper to install two new capacitors.

:P

steve

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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: Apr Thu 09, 2020 12:32 pm 
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Dutch Rabbit wrote:
it would be cheaper to install two new capacitors.

:P

steve


I am sure John would appreciate that prior to shipping him the lefty. :D

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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: Apr Fri 10, 2020 5:46 pm 
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well, everything has a price :P .

i have to say no on the lefty though.

it was my great aunt gladys's set who lived across the yard. i used to play it all the time when i went to her house, which was nearly every day.

the 544 sat on her kitchen counter for as long as i can remember.

she lived to age 99 in 2011.

steve

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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: Apr Fri 10, 2020 6:39 pm 
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Dutch Rabbit wrote:
well, everything has a price :P .
i have to say no on the lefty though.
it was my great aunt gladys's set who lived across the yard. i used to play it all the time when i went to her house, which was nearly every day.
the 544 sat on her kitchen counter for as long as i can remember.
she lived to age 99 in 2011.
steve
That's terrific for you to have the ***actual radio*** you listened to as a kid!
A family heirloom!

I own two radios which are the exact same models my parents had when I was a child: An RCA 6-XD-5 and an RCA 3-X-533. However neither is the actual "family original radio."

-EB

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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: Apr Fri 10, 2020 7:07 pm 
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Last summer I got out a Realistic DX-400 which had not been used for about five years. Don't laugh--it was something my mom bought as a birthday present for my grandfather about 30 years ago and since both of them are gone now, I'm taking care of the radio for them. It has never been repaired and has all its original electrolytics in it.

Anyway, when I turned it on, the only thing that worked was the pilot light. No sound, no display, no nothing. After messing with every switch and control for five minutes, I started to take the back off while it was still plugged in, and it started crackling. The crackle soon turned to very low, weak audio. After a bit the display popped in. Then the shortwave bands started working followed by the FM. But a couple of hours later, the audio was still a bit distorted. The fact that the radio had made good progress "rising from the dead" and was now essentially working was a good indication that it was suffering from de-formed electrolytics which were now bouncing back.

So I left it on top of the washing machine, playing in its weakened state, for 24 hours. At the end of that time the distortion was completely gone and it was working like new. Six months later it is still going strong. Not saying that everything should be or can be fixed this way, but if you are going to reform caps "in circuit" after long periods of disuse, it may take more than an hour or two. On the other hand, if they haven't recovered after running for 24 hours, they probably aren't going to.

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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: Apr Sat 11, 2020 3:27 am 
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thanks chris,

this guy is going to get new capacitors.

steve

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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: Apr Sat 11, 2020 3:28 am 
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EB,

i will post a few more pics of some family hierlooms this wknd.

steve

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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: May Fri 01, 2020 4:37 am 
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family heirlooms from the grandparents

the detrola was my mother's mother's radio. this is the set that i accidentally flipped the switch to SW when i was a little boy and my interest was sparked for the next 30 years. i managed to hear and QSL around 200 radio countries according to the North American Short Wave Association Country List. they were all national broadcasts like Radio Japan, Radio Baghdad, etc., no "hams".

flipping that switch in 1980 gave me a lifetime of geography, history, language, political, and musical, lessons that no university could provide.

the zenith FM radio was my dad's mother's radio.

the RCA was my grandparents' HiFi on my dad's side. i used to stand up on that little red chair and watch the records spin and listen to them for hours when i was a little boy.

steve


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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: May Fri 01, 2020 7:50 am 
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I did see a recommendation from I think ABBY? That you powered electrolytic caps at least once in two years. If I have NOs caps, or a refitted radio that has been sitting a while, in the case of a radio I will power B+ only with the reformer that has a stepper & gradually build up the volts to give them the chance to reform before powering the radio fully. Individual caps similar.

The reformer was originally made to catch out the often new duds that like to get to a point and then become a conductor, but has proved useful in other spheres.

Marc


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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: May Fri 01, 2020 3:43 pm 
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the sets are on s rotating basis now and will be played a couple times a year.

restored as5 sets will get plugged in and turned on.

the 10 or so transformered sets that have sat will be slowly brought up on a variac.

once all get into a regular rotation, they will be turned on just like mama did back in the day.

steve

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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: May Fri 01, 2020 3:46 pm 
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Chris108 wrote:
Last summer I got out a Realistic DX-400 which had not been used for about five years. Don't laugh--it was something my mom bought as a birthday present for my grandfather about 30 years ago and since both of them are gone now, I'm taking care of the radio for them. It has never been repaired and has all its original electrolytics in it.

Anyway, when I turned it on, the only thing that worked was the pilot light. No sound, no display, no nothing. After messing with every switch and control for five minutes, I started to take the back off while it was still plugged in, and it started crackling. The crackle soon turned to very low, weak audio. After a bit the display popped in. Then the shortwave bands started working followed by the FM. But a couple of hours later, the audio was still a bit distorted. The fact that the radio had made good progress "rising from the dead" and was now essentially working was a good indication that it was suffering from de-formed electrolytics which were now bouncing back.

So I left it on top of the washing machine, playing in its weakened state, for 24 hours. At the end of that time the distortion was completely gone and it was working like new. Six months later it is still going strong. Not saying that everything should be or can be fixed this way, but if you are going to reform caps "in circuit" after long periods of disuse, it may take more than an hour or two. On the other hand, if they haven't recovered after running for 24 hours, they probably aren't going to.

No idea what your problem was but I doubt it's electrolytics. A reforming electrolytic, drawing enough current that drags down B+ to point of no play, WILL overheat transformer and/or rectifier badly.

I dragged out one of my Warcos that's been unused for last two years, it's reception is intermittent but mostly dead, audio is up without issue. That isn't a electrolytic issue.

I have seen radios with weakish rectifier and caps needing reformed gradually increase B+ till point they'll finally play. I have a 1940 silvertone with original electrolytic that fits this description. It's twin also has it's orig electrolytic(one section jumpered), that one was a daily player for a couple years. I can't say they'll play today, as like Warco haven't been on in a couple years.

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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: May Fri 01, 2020 4:05 pm 
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If stored or not powered for a length of time, electrolytics need to be reformed by slowly increasing the voltage to them. Too quick of an application of voltage risks a surge of current through them, and possible damage.

It helps to understand how they work. When we are talking about aluminum can electrolytics, the negative element is the case, made of aluminum. The electrolyte is contained and sealed inside that can and as long as the seal remains intact, the electrolyte is still good. The can is mechanically and electrically separated from the other conductor with the electrolyte between.

Initially, as when first manufactured, (and before any voltage is applied) there could be conduction between the two conductors. As DC voltage is properly applied the electrolyte oxidizes the inside surface of the can with an extremely thin layer of aluminum oxide, or sapphire. Sapphire is an excellent non-conductor, or de-electric. To get more capacitance, the surface of the can and sometimes the inner electrode are roughened to increase their surface area.

Applying a voltage in the opposite direction, destroys the sapphire layer by reversing the oxidization of the surface, and hence the electrolyte would conduct, causing a shorted condition. Also, over a long period of time, if no voltage is applied in the proper direction, the sapphire layer very slowly decomposes.

On radios that have sat for years, best to apply a rising voltage instead of an instant voltage. Several seconds rise time is sufficient. On electrolytics that have been stored for long periods of time, they can be reformed by inserting a resistor in series while applying a properly polarized DC working voltage to them.


Last edited by startgroove on May Fri 01, 2020 5:47 pm, edited 1 time in total.

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 Post subject: Re: An Indication of a "Reforming Capactior" Questions
PostPosted: May Fri 01, 2020 4:27 pm 
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Hi Tom,

The DX400 is a microprocessor controlled multiband portable from the 1980s, certainly old enough to have deformed electrolytics after sitting around unused for several years but new enough that replacing all the caps should not be necessary. There are a couple dozen electrolytics on a tightly packed board in a small case, so this thing was not built for easy service. I do not know which electrolytic(s) had deformed, but since the radio did not hum or show signs of power supply overload, it was probably an audio bypass or coupling cap that caused the immediate problem.

The point I was making is that if there is nothing otherwise wrong with them, electrolytics can often be re-formed in circuit simply by running the device for 24 hours. The radio worked fine before it was put away, so the capacitors were not defective, just deformed. I do the same with my HP and Tektronix test equipment, some of which goes a year or two between uses, i.e. just leave it on for a day to reform the caps before checking calibration and putting it into operation. (With scopes and other instruments which have CRTs, I make sure the beams are turned down during the run-in). I do not do this with equipment I've just acquired, as I usually do not know how long it has been since it last worked. In that case, a careful pre-powering check and slow-starting the voltage is usually necessary.

In my experience, any electronic equipment that is still acting up after 24 hours of burning in probably has caps too far gone to reform, or some other problem. The other thing is, if you then put the equipment aside for a while, say six months, what happens? Does it come right up or does it need to reform again? If it bounces right back the capacitors are probably okay. But if they've already deformed again, they are on their last legs. Fortunately my DX400 showed no signs of deforming after several more months of non-use and came right up again.

Re your Warco, agree that if you've got good audio, the power supply circuit is probably fine and the problem is in the converter or IF stages.

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