|
Old Paper Caps - Are they Always Bad?
I have several postings here about an SX-101a I am restoring. Up to
now I have done consumer radios, TVs, and an SX-71. I found the majority of the paper caps (wax or molded) to be bad in them. By bad, I found them to be out of tolerance (usually reading high on my old 60hz reactance bridge meter) and showing significant leakage at rated voltage. So now I start on the SX-101a and wouldn't you know it the first 4 paper caps I pulled check perfectly in all respects. These do appear to be a much higher quality cap than those I have seen to date, but paper they are. So if 4 out of 4 are good, do I need to replace all the paper caps in this unit? Perhaps this radio never saw much humidity, and coupling that with higher quality parts they might still be just fine. I am tempted to reinstall the ones I just pulled to keep the vintage look. I really don't know how to test the caps in circuit individually unless I pull one lead, and then you are half way to replaced anyway, so if there is high likelyhood of some bad ones out there, I might as well replace them all. Are there certain circuit locations more prone to fail? I have stopped further work until I get some feedback on this. Dan |
"geojunkie" wrote in message om... Are the good caps C-D Black Cats? Those are mylar. Don't ever trust those pink Tiny Chiefs or Black Beauties. Frank Dresser |
I replace caps that need to be replaced. I have found that every
electrolytic that has a small voltage rating is bad and they get changed out without even thinking. I have found a lot of electrolytic that are higher voltage units to be higher in value but then after they get reformed end up reading within tolerance. I have only started looking at leakage and so far after a good reforming they seem to be what I call good enough to use. Of course some will not reform and they get trashed. I have found just as many silver mica and ceramic disk caps bad as I have found black beauty caps and the other paper caps. . Unless a cap is in a part of the circuit where a failure would cause a major failure like in the 75A4 where it will take out a filter I don't even think of swapping them out unless my testing shows a problem with that part of the circuit or the part is literally falling apart. My feeling about the caps of old was that quality control was there major problem. I expect that assemble of these caps was a big factor and that depending on who did the assemble some ended up never being a problem and some got contamination during manufact and ended up failing early in there life. My two cents worth, Ron WA0KDS geojunkie wrote: I have several postings here about an SX-101a I am restoring. Up to now I have done consumer radios, TVs, and an SX-71. I found the majority of the paper caps (wax or molded) to be bad in them. By bad, I found them to be out of tolerance (usually reading high on my old 60hz reactance bridge meter) and showing significant leakage at rated voltage. So now I start on the SX-101a and wouldn't you know it the first 4 paper caps I pulled check perfectly in all respects. These do appear to be a much higher quality cap than those I have seen to date, but paper they are. So if 4 out of 4 are good, do I need to replace all the paper caps in this unit? Perhaps this radio never saw much humidity, and coupling that with higher quality parts they might still be just fine. I am tempted to reinstall the ones I just pulled to keep the vintage look. I really don't know how to test the caps in circuit individually unless I pull one lead, and then you are half way to replaced anyway, so if there is high likelyhood of some bad ones out there, I might as well replace them all. Are there certain circuit locations more prone to fail? I have stopped further work until I get some feedback on this. Dan |
"geojunkie" wrote in message om... It's easy to figure how much capacitor leakage would cause an excessive grid voltage, a reduced screen voltage or plate voltage. It's a simple ohm's law problem. Don't forget the power leaky bypass capacitors have to dissapate. Cathode bypasses can get very leaky before causing problems. But I'd be surprised if there are any 40+ year old paper caps around that can meet a fairly loose throw away standard now. Say 1 microamp per microfarad at it's rated voltage. What year was your SX 101 made? Mylar caps started showing up around 1960. Even my SW 500 (S 120) had several good quality mylar C-D Black Cats. Also, there was an early 60s version of the Sprague Black Beauty which was paper-mylar rather than paper-oil. The paper-mylar cap was quite reliable. Frank Dresser |
Frank Dresser wrote:
"geojunkie" wrote in message om... It's easy to figure how much capacitor leakage would cause an excessive grid voltage, a reduced screen voltage or plate voltage. It's a simple ohm's law problem. Don't forget the power leaky bypass capacitors have to dissapate. Cathode bypasses can get very leaky before causing problems. But I'd be surprised if there are any 40+ year old paper caps around that can meet a fairly loose throw away standard now. Say 1 microamp per microfarad at it's rated voltage. What year was your SX 101 made? Mylar caps started showing up around 1960. Even my SW 500 (S 120) had several good quality mylar C-D Black Cats. Also, there was an early 60s version of the Sprague Black Beauty which was paper-mylar rather than paper-oil. The paper-mylar cap was quite reliable. Frank Dresser Here's an excellent way to determine if paper caps should be replaced. Count the number of caps in the radio and divide by the number of times you want to go in and re-troubleshoot. If the quotient is equal to or less than the original number of caps then they should be replaced. Hope this helps, Bill |
Here's an excellent way to determine if paper caps should be replaced.
Count the number of caps in the radio and divide by the number of times you want to go in and re-troubleshoot. If the quotient is equal to or less than the original number of caps then they should be replaced. Hope this helps, Bill Should we be getting vibes you feel strongly about this? Avery W3AVE Potomac, Md. |
I'll concur with the other comments. I (personally) wholesale change out
caps when one or more go out and/or when I first check out a radio before powering up (and find bad ones). Having said that, I have found both extremes in older radios. For example, my HQ-120 was dead, blew fuses, and had about 500 ohms plate resistance presented to the PS. All caps were changed and the radio in now fine. In my National receivers, the Black-Beauties split, leak oil, short, and are generally very disagreeable components. My BC-669 transceiver (circa 1944) required all the mica caps to be replaced, something I would not have expected, until now. Sangamo's, included! There aren't any caps that are bullet-proof after 50 years. My SX-28 still has most of the wax/paper caps working just fine. One of these days, though............ Finally, the sage advice to change those parts which will precipitate other, perhaps worse, failures is mandatory. Its just not worth the risk and to try and find some old IF can, etc. if one smokes, after the fact. My take on the issue... 73 de K3HVG geojunkie wrote: I have several postings here about an SX-101a I am restoring. Up to now I have done consumer radios, TVs, and an SX-71. I found the majority of the paper caps (wax or molded) to be bad in them. By bad, I found them to be out of tolerance (usually reading high on my old 60hz reactance bridge meter) and showing significant leakage at rated voltage. So now I start on the SX-101a and wouldn't you know it the first 4 paper caps I pulled check perfectly in all respects. These do appear to be a much higher quality cap than those I have seen to date, but paper they are. So if 4 out of 4 are good, do I need to replace all the paper caps in this unit? Perhaps this radio never saw much humidity, and coupling that with higher quality parts they might still be just fine. I am tempted to reinstall the ones I just pulled to keep the vintage look. I really don't know how to test the caps in circuit individually unless I pull one lead, and then you are half way to replaced anyway, so if there is high likelyhood of some bad ones out there, I might as well replace them all. Are there certain circuit locations more prone to fail? I have stopped further work until I get some feedback on this. Dan |
AComarow wrote:
Here's an excellent way to determine if paper caps should be replaced. Count the number of caps in the radio and divide by the number of times you want to go in and re-troubleshoot. If the quotient is equal to or less than the original number of caps then they should be replaced. Hope this helps, Bill Should we be getting vibes you feel strongly about this? Avery W3AVE Potomac, Md. Only vibes, Ave? Maybe I wasn't clear enough! :-) Seriously, I question the logic of say encountering 20 caps in a 50-year old radio and half of them have gone bad and then leaving the other half. "Bad" is a relative term depending where it is in the circuit and how much leakage you can tolerate but the fact is that the paper is slowly deteriorating because of inherent acids and is only gonna get worse with time. So, you can replace them now or later. I enjoy replacing caps, and I restuff the paper ones, and I really don't mind doing so. Might as well unless you're in it for a business where your time equals money. -Bill |
"Are the good caps C-D Black Cats? Those are mylar.
Don't ever trust those pink Tiny Chiefs or Black Beauties." This is an SX-101a that I believe is near 1962, as the knobs match later receivers like the SX-115 and SX-117. The paper caps are pink Tiny Chief 600v, and molded black caps that are marked only with stripes... no lettering of any kind. I do see a "P" molded into tiny circles on one side and a "2" in similar circles on the other side. What brand of black caps are these? The parts list calls them both paper caps and never mentions mylar. Sounds like you would tend to replace them all based on this. I have been using tubular polypropylene 630v for replacements, the yellow ones. I notice some seem to love the orange drops. Is there a difference worth worrying about? I did find a 10w wirewound heater located under the RF amp, mixer and 1st osc tubes that was almost shorted and most of the components over it are discolored. This thing is about 6" long, I think I will put a string of maybe three new power resistors of 1/3 the value in the metal casing and hope this distributes the heat evenly enough. This heater is on line anytime the receiver is plugged in, as is the oscillator filament. |
geojunkie wrote:
"Are the good caps C-D Black Cats? Those are mylar. Don't ever trust those pink Tiny Chiefs or Black Beauties." This is an SX-101a that I believe is near 1962, as the knobs match later receivers like the SX-115 and SX-117. The paper caps are pink Tiny Chief 600v, and molded black caps that are marked only with stripes... no lettering of any kind. I do see a "P" molded into tiny circles on one side and a "2" in similar circles on the other side. What brand of black caps are these? The parts list calls them both paper caps and never mentions mylar. I have seen the "2 in a circle" on most Sprague capacitors. -- Merry Christmas! Take care, and God bless. Michael A. Terrell Central Florida |
Only vibes, Ave? Maybe I wasn't clear enough!
:-) Seriously, I question the logic of say encountering 20 caps in a 50-year old radio and half of them have gone bad and then leaving the other half. "Bad" is a relative term depending where it is in the circuit and how much leakage you can tolerate but the fact is that the paper is slowly deteriorating because of inherent acids and is only gonna get worse with time. So, you can replace them now or later. I enjoy replacing caps, and I restuff the paper ones, and I really don't mind doing so. Might as well unless you're in it for a business where your time equals money. -Bill I totally agree. Unfortunately, when I start thinking about recapping some of the old communications receivers I have around and what that would involve, my inclination is to put it off, and off, and off. Removing the sliding coil catacomb from an NC-2-40D to get at the caps lurking beneath is one of these little nightmares--I can take anything out, but putting it back the right way often challenges my modest mechanical skills. This group probably boasts hundreds of individuals who rub their hands with glee when they face these jobs. Me, I'd like a wide-open chassis, please. Not that this has anything to do with your logic, which is impeccable as always.... Avery W3AVE Potomac, Md. |
"geojunkie" wrote in message om... This is an SX-101a that I believe is near 1962, as the knobs match later receivers like the SX-115 and SX-117. The paper caps are pink Tiny Chief 600v, and molded black caps that are marked only with stripes... no lettering of any kind. I do see a "P" molded into tiny circles on one side and a "2" in similar circles on the other side. What brand of black caps are these? The parts list calls them both paper caps and never mentions mylar. The striped caps are probably Sprague Black Beauties. I have some Black Beauties and all have a 2 molded in recesses on one side, and various letters molded in recesses on the other side. If one of the capacitor's leads are soldered into a nipple on one side, they're oil filled. I don't know about the SX 101's part list, but I do know the term "paper capacitor" lasted into the 70's as a generic term for film capacitors in such technical writings as the ARRL Handbook. Sounds like you would tend to replace them all based on this. I have been using tubular polypropylene 630v for replacements, the yellow ones. I notice some seem to love the orange drops. Is there a difference worth worrying about? I'd probably crack one or two open for curiosity's sake. Mylar is quite clear and paper is translucent brown. If they turned out to be paper, I'd double check my testing procedure. Paper caps had detectable leakage even when new. If they are paper, I'd change them. If they are mylar, I wouldn't worry unless troubleshooting pointed out a problem. Either the Orange Drops or the yellow caps are excellent replacements. I prefer the yellow caps because they are a bit more compact and they have longer axial leads. They are usually easier to work with. I'm not sure the yellow polyporpylene caps you have are the same size as the yellow mylars I like, however. The only problem with the yellow caps is they aren't resistant to a hot soldering tip. No problem, once I learned to be careful. I did find a 10w wirewound heater located under the RF amp, mixer and 1st osc tubes that was almost shorted and most of the components over it are discolored. This thing is about 6" long, I think I will put a string of maybe three new power resistors of 1/3 the value in the metal casing and hope this distributes the heat evenly enough. This heater is on line anytime the receiver is plugged in, as is the oscillator filament. A wirewound almost shorted? That's odd. I don't know the details of the SX 101, but I'm wondering if the resistor is there as a temperature regulator. If so, it might have a high positive temperature coefficent, and it's cold resistance would be much lower than it's hot resistance. Frank Dresser |
Frank Dresser wrote:
"geojunkie" wrote in message om... It's easy to figure how much capacitor leakage would cause an excessive grid voltage, a reduced screen voltage or plate voltage. It's a simple ohm's law problem. Don't forget the power leaky bypass capacitors have to dissapate. Cathode bypasses can get very leaky before causing problems. But I'd be surprised if there are any 40+ year old paper caps around that can meet a fairly loose throw away standard now. Say 1 microamp per microfarad at it's rated voltage. What year was your SX 101 made? Mylar caps started showing up around 1960. Even my SW 500 (S 120) had several good quality mylar C-D Black Cats. Also, there was an early 60s version of the Sprague Black Beauty which was paper-mylar rather than paper-oil. The paper-mylar cap was quite reliable. Frank Dresser My SX-122 (circa-1963) has mylar caps'. I haven't changed any of them. I didn't find any of the paper/oil types. The remaining caps' are ceramic disc and a few micas. I did change the power filter caps' just to be safe. BTW- The SX-122 was the last of the Hallicrafters 'SX' series of receivers produced under the original Halligan family ownership. The SX-122'A' (1967-1969) was made under 'Rockwell' management. They increased the price by $100 without any significant improvements in the design or performance. -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
- - Bill - - wrote:
So, you can replace them now or later. I enjoy replacing caps, and I restuff the paper ones, and I really don't mind doing so. Might as well unless you're in it for a business where your time equals money. Where can one learn about the art of 'restuffing' paper caps'? I saved all the old ones from recapping my SX-100. Maybe I'll restuff them some day. -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Frank Dresser wrote:
The striped caps are probably Sprague Black Beauties. I have some Black Beauties and all have a 2 molded in recesses on one side, and various letters molded in recesses on the other side. If one of the capacitor's leads are soldered into a nipple on one side, they're oil filled. Was the oil 'PCB'? -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
starman wrote:
- - Bill - - wrote: So, you can replace them now or later. I enjoy replacing caps, and I restuff the paper ones, and I really don't mind doing so. Might as well unless you're in it for a business where your time equals money. Where can one learn about the art of 'restuffing' paper caps'? I saved all the old ones from recapping my SX-100. Maybe I'll restuff them some day. I hope you aren't being facetious and yanking my chain. Its really quite easy to do although a bit messy and tedious and its much easier to do a whole batch at one time rather than one off. A heat-gun is the best way to unload the old casing. Dig out the 1/8" or so of wax at each end and save it. Caveat here is that some brands use an epoxy type filler on the ends. Apply heat for maybe 20-30 seconds, use gloves/rags/whatever and grab one lead and yank it out. Most often the lead alone will come out (that tells you something about the crappo internal connection integrity). So try the other end. Same thing may happen. So use a screwdriver or something to poke the guts out of the cardboard tube. If its still warm it should push right thru. If you need extra long leads chop short one lead of the new cap and solder on an appropriate amount of wire so that the connection will be hidden inside the original tube. Install the new cap in the cardboard tube and squirt in some hot melt glue at one end. Let that cool enough so as to not run and do the other side. Fill to almost full. Once its all cooled and settled, take some of the original chunks of wax you saved in the first step...place on the end and use an old soldering pencil to melt it around to replicate the end seal. Done deal. The aesthetics of just how clean you want the exterior are up to you. You can smooth out the grubby old wax with the heat gun or clean it up with WD-40 or a combination of the two. Its an addictive part of restoration. After you've done it a couple of times and see the nice original looking results with the comfort of knowing those caps aren't going to crap out in your lifetime you'll never go back to plain old yellow caps or orange drops or other "glo-brite" colors that look so inappropriate underneath an old chassis. HTH, -Bill |
- - Bill - - wrote:
starman wrote: - - Bill - - wrote: So, you can replace them now or later. I enjoy replacing caps, and I restuff the paper ones, and I really don't mind doing so. Might as well unless you're in it for a business where your time equals money. Where can one learn about the art of 'restuffing' paper caps'? I saved all the old ones from recapping my SX-100. Maybe I'll restuff them some day. I hope you aren't being facetious and yanking my chain. Its really quite easy to do although a bit messy and tedious and its much easier to do a whole batch at one time rather than one off. A heat-gun is the best way to unload the old casing. Dig out the 1/8" or so of wax at each end and save it. Caveat here is that some brands use an epoxy type filler on the ends. Apply heat for maybe 20-30 seconds, use gloves/rags/whatever and grab one lead and yank it out. Most often the lead alone will come out (that tells you something about the crappo internal connection integrity). So try the other end. Same thing may happen. So use a screwdriver or something to poke the guts out of the cardboard tube. If its still warm it should push right thru. If you need extra long leads chop short one lead of the new cap and solder on an appropriate amount of wire so that the connection will be hidden inside the original tube. Install the new cap in the cardboard tube and squirt in some hot melt glue at one end. Let that cool enough so as to not run and do the other side. Fill to almost full. Once its all cooled and settled, take some of the original chunks of wax you saved in the first step...place on the end and use an old soldering pencil to melt it around to replicate the end seal. Done deal. The aesthetics of just how clean you want the exterior are up to you. You can smooth out the grubby old wax with the heat gun or clean it up with WD-40 or a combination of the two. Its an addictive part of restoration. After you've done it a couple of times and see the nice original looking results with the comfort of knowing those caps aren't going to crap out in your lifetime you'll never go back to plain old yellow caps or orange drops or other "glo-brite" colors that look so inappropriate underneath an old chassis. HTH, -Bill My query was genuine. I've never considered the possibility of putting new cap's inside the old casings, at least not for paper ones. I have experimented with gutting and refilling the large electrolytic cans. Thanks for the tips. -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
The striped caps are probably Sprague Black Beauties. I have some Black
Beauties and all have a 2 molded in recesses on one side, and various letters molded in recesses on the other side. If one of the capacitor's leads are soldered into a nipple on one side, they're oil filled. Was the oil 'PCB'? Plain old mineral oil. PCBs were too expensive for consumer products, and were always identified by trade names like Clorinol. Hyvol, Dykanol, Inerteen. 73, Alan |
"starman" wrote in message
... - - Bill - - wrote: So, you can replace them now or later. I enjoy replacing caps, and I restuff the paper ones, and I really don't mind doing so. Might as well unless you're in it for a business where your time equals money. Where can one learn about the art of 'restuffing' paper caps'? I saved all the old ones from recapping my SX-100. Maybe I'll restuff them some day. The Early Television web site has details for retaining the "look" of the original paper capacitor components -- but using modern components. http://www.earlytelevision.org/capreplace.html w9gb |
starman wrote:
- - Bill - - wrote: So, you can replace them now or later. I enjoy replacing caps, and I restuff the paper ones, and I really don't mind doing so. Might as well unless you're in it for a business where your time equals money. Where can one learn about the art of 'restuffing' paper caps'? I saved all the old ones from recapping my SX-100. Maybe I'll restuff them some day. It isn't hard, use a heat gun to soften up the old wax, then with pliers pull the old cap out of the tube by the lead (hold the hot tube with a shop towel). If the lead comes off without pulling out the insides, you can use something like a piece of dowel rod to push the insides out. Put the new cap in the tube and use hot glue to seal it up. You can get colored glue sticks that will look much like the old wax. |
Quote:
It has been my experience that micas and ceramics give less trouble from a statistical standpoint. However, they can certainly fail. The older "paper" dielectric tubular capacitors were not top notch performers from an electrical standpoint when they were newly manufactured. The commonly known capacitor parameters such as insulation resistance, Q, series R, etc. have certainly improved when applied to the modern dielectrics of today's capacitors. Having stated this I recommend replacing "paper" capacitors whenever they are encountered just to take advantage of the improved performance of a modern unit. One of the other respondents also gave good advice when he related to future troubles and "callbacks" that might well occur when old units are left in place. Good luck with your restorations. Dr. T |
| All times are GMT +1. The time now is 03:51 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com