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#1
December 26th 03, 02:09 PM
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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. |
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#2
December 26th 03, 02:28 PM
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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 |
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#3
December 26th 03, 04:40 PM
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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. |
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#4
December 27th 03, 07:01 AM
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- - 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! =----- |
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#5
December 27th 03, 06:56 AM
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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! =----- |
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#6
December 26th 03, 02:18 PM
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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 |
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#7
December 15th 08, 03:32 AM
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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 |
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