Home |
Search |
Today's Posts |
|
#1
![]() |
|||
|
|||
![]()
I always heard about leaky caps being a problem with boatanchors, other than
checking for the capacitor value is there a way to check if its a "leaky cap" using just a multitester or voltmeter? Thanks.....gil |
#2
![]() |
|||
|
|||
![]()
gil wrote:
I always heard about leaky caps being a problem with boatanchors, other than checking for the capacitor value is there a way to check if its a "leaky cap" using just a multitester or voltmeter? Thanks.....gil There's some good capacitor testers around but as a rule on older BAs (30s-40s) if it doesn't pass an ohmmeter test you need not go any further. I chuck anything over about 1 Meg of leakage which tends to be most all wax/paper caps from that era. The digital voltmeters often have a capacitance test function but are thrown off in the presence of leakage. Again, if it doesn't measure right, out she goes. The problem is due to the breakdown of the paper dielectric inside. For the most part thats inevitable in spite of how well sealed it is. Some of the high-end mil-spec metal cased guys have survived but thats about all. The rest are hit-and-miss. In later gear, say the 50s, the "good" rate is much improved but certain types like the banded black beauties are notoriously bad as are those pink plastic ones found in 50s/60s Hallicrafters gear. The debate lingers on just how much performance degradation and reliability can be tolerated since the bad caps may not have a particular detrimental effect *today* depending on where in the circuit they are used. I suppose it depends whether or not you are "restoring" or "repairing". I cross-posted this to rec.antiques.radio+phono so you could catch some other opinions. Good luck! -Bill |
#3
![]() |
|||
|
|||
![]()
I would take the approach that failing the ohmmeter test means definitely
bad, but even passing the ohmmeter test means nothing better than "doubtful." I used to try to analyze the importance of leakage in a particular part, and try to "calculate " the leakage based on circuit voltages. For example, I'd measure the grid voltage and from that try to guess whether the coupling cap was too leaky. I also tried the ohmmeter thing. I gave up. I have since used a Heath IT-28 capacitor tester, with excellent results. The criteria it uses are that a good electrolytic leaks less than 2 mA, a "small" electrolytic less that 15 uA, and a paper-mica-polyester etc.less than 2 uA AT THE RATED VOLTAGE. The ability to apply any more than a very small voltage to the cap is the downfall of the ohmmeter methods. I have tried digital capacitor testers but they have a hard time identifying leakage, and often just read the wrong value of capacitance. For testing boatanchor-era caps, I would strongly suggest that you get one of the same-era capacitor bridges that let you test with real voltage applied. I like the Heath, but I have also used the Sprague and I am sure many others are just as good. I went through my junk box and probably threw out 1/2 of what I thought were good caps. As other posters have indicated the banded Black Beauties are ALL bad, the ones with yellow lettering are ALMOST all bad, but surprisingly the ones with pink lettering are still largely OK. Anything dipped in wax is shot. Anyway, my vote is for a good, old cap bridge. Now, if someone would just invent an LED substitute for the 6E5s in these things. "--exray--" wrote in message ... gil wrote: I always heard about leaky caps being a problem with boatanchors, other than checking for the capacitor value is there a way to check if its a "leaky cap" using just a multitester or voltmeter? Thanks.....gil There's some good capacitor testers around but as a rule on older BAs (30s-40s) if it doesn't pass an ohmmeter test you need not go any further. I chuck anything over about 1 Meg of leakage which tends to be most all wax/paper caps from that era. The digital voltmeters often have a capacitance test function but are thrown off in the presence of leakage. Again, if it doesn't measure right, out she goes. The problem is due to the breakdown of the paper dielectric inside. For the most part thats inevitable in spite of how well sealed it is. Some of the high-end mil-spec metal cased guys have survived but thats about all. The rest are hit-and-miss. In later gear, say the 50s, the "good" rate is much improved but certain types like the banded black beauties are notoriously bad as are those pink plastic ones found in 50s/60s Hallicrafters gear. The debate lingers on just how much performance degradation and reliability can be tolerated since the bad caps may not have a particular detrimental effect *today* depending on where in the circuit they are used. I suppose it depends whether or not you are "restoring" or "repairing". I cross-posted this to rec.antiques.radio+phono so you could catch some other opinions. Good luck! -Bill |
#4
![]() |
|||
|
|||
![]()
I picked up a highly-regarded Sprague "Tel-Ohmike TO-4" R-C bridge,
and found that it was loaded with Sprague Black Beauty capacitors. It's funny that I'll have to first re-cap the bridge before I can use it to test capacitors. 73, Ed K4PF |
#5
![]() |
|||
|
|||
![]()
I picked up a highly-regarded Sprague "Tel-Ohmike TO-4" R-C bridge,
and found that it was loaded with Sprague Black Beauty capacitors. It's funny that I'll have to first re-cap the bridge before I can use it to test capacitors. 73, Ed K4PF |
#6
![]() |
|||
|
|||
![]()
In article , "BFoelsch"
writes: For testing boatanchor-era caps, I would strongly suggest that you get one of the same-era capacitor bridges that let you test with real voltage applied. I like the Heath, but I have also used the Sprague and I am sure many others are just as good. I use the venerable Eico 950A bridge and leakage tester. You can dial up any voltage up to around 500 and observe leakage on the magic eye tube; for 'lytics, a neon bulb in series is subbed for the eye tube. Once you charge the cap up to rated voltage, the eye or bulb should show nothing. Great for reforming lytics too. And the bridge is pretty accurate for measurements. But still, before cutting one end loose to check it, I find it worthwhile to check grid and screen voltages in a radio to see if a cap is really leaking enough to throw things off. --Mike K. Oscar loves trash, but hates Spam! Delete him to reply to me. |
#7
![]() |
|||
|
|||
![]()
In article , "BFoelsch"
writes: For testing boatanchor-era caps, I would strongly suggest that you get one of the same-era capacitor bridges that let you test with real voltage applied. I like the Heath, but I have also used the Sprague and I am sure many others are just as good. I use the venerable Eico 950A bridge and leakage tester. You can dial up any voltage up to around 500 and observe leakage on the magic eye tube; for 'lytics, a neon bulb in series is subbed for the eye tube. Once you charge the cap up to rated voltage, the eye or bulb should show nothing. Great for reforming lytics too. And the bridge is pretty accurate for measurements. But still, before cutting one end loose to check it, I find it worthwhile to check grid and screen voltages in a radio to see if a cap is really leaking enough to throw things off. --Mike K. Oscar loves trash, but hates Spam! Delete him to reply to me. |
#8
![]() |
|||
|
|||
![]()
I would take the approach that failing the ohmmeter test means definitely
bad, but even passing the ohmmeter test means nothing better than "doubtful." I used to try to analyze the importance of leakage in a particular part, and try to "calculate " the leakage based on circuit voltages. For example, I'd measure the grid voltage and from that try to guess whether the coupling cap was too leaky. I also tried the ohmmeter thing. I gave up. I have since used a Heath IT-28 capacitor tester, with excellent results. The criteria it uses are that a good electrolytic leaks less than 2 mA, a "small" electrolytic less that 15 uA, and a paper-mica-polyester etc.less than 2 uA AT THE RATED VOLTAGE. The ability to apply any more than a very small voltage to the cap is the downfall of the ohmmeter methods. I have tried digital capacitor testers but they have a hard time identifying leakage, and often just read the wrong value of capacitance. For testing boatanchor-era caps, I would strongly suggest that you get one of the same-era capacitor bridges that let you test with real voltage applied. I like the Heath, but I have also used the Sprague and I am sure many others are just as good. I went through my junk box and probably threw out 1/2 of what I thought were good caps. As other posters have indicated the banded Black Beauties are ALL bad, the ones with yellow lettering are ALMOST all bad, but surprisingly the ones with pink lettering are still largely OK. Anything dipped in wax is shot. Anyway, my vote is for a good, old cap bridge. Now, if someone would just invent an LED substitute for the 6E5s in these things. "--exray--" wrote in message ... gil wrote: I always heard about leaky caps being a problem with boatanchors, other than checking for the capacitor value is there a way to check if its a "leaky cap" using just a multitester or voltmeter? Thanks.....gil There's some good capacitor testers around but as a rule on older BAs (30s-40s) if it doesn't pass an ohmmeter test you need not go any further. I chuck anything over about 1 Meg of leakage which tends to be most all wax/paper caps from that era. The digital voltmeters often have a capacitance test function but are thrown off in the presence of leakage. Again, if it doesn't measure right, out she goes. The problem is due to the breakdown of the paper dielectric inside. For the most part thats inevitable in spite of how well sealed it is. Some of the high-end mil-spec metal cased guys have survived but thats about all. The rest are hit-and-miss. In later gear, say the 50s, the "good" rate is much improved but certain types like the banded black beauties are notoriously bad as are those pink plastic ones found in 50s/60s Hallicrafters gear. The debate lingers on just how much performance degradation and reliability can be tolerated since the bad caps may not have a particular detrimental effect *today* depending on where in the circuit they are used. I suppose it depends whether or not you are "restoring" or "repairing". I cross-posted this to rec.antiques.radio+phono so you could catch some other opinions. Good luck! -Bill |
#9
![]() |
|||
|
|||
![]()
On Sun, 19 Oct 2003 10:12:52 -0400, --exray-- wrote:
The digital voltmeters often have a capacitance test function but are thrown off in the presence of leakage. Again, if it doesn't measure right, out she goes. I have both a dedicated Capacitor meter and a multimeter that measures capacitance. Both do the same thing when presented with leaky caps. The cap will invariably read two or three times more than what its value is supposed to be. I have tested brand new electrolytics and have found them to be as much as 50% off rated capacity. Small coupling and bypass caps, though are usually right on the money if they're good. -Scott To reply to this message via e-mail, replace "fromrarp" in the e-mail address with "scott" |
#10
![]() |
|||
|
|||
![]() "Scott W. Harvey" wrote in message ... [snip] I have tested brand new electrolytics and have found them to be as much as 50% off rated capacity. Small coupling and bypass caps, though are usually right on the money if they're good. -Scott That's interesting. I've checked some new electrolytics with my old Heathkit cap checker, and they are almost always within 20% or so of the indicated value. I'll check more later and see if it still holds true. Frank Dresser |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
Thread | Forum | |||
Weather caps | Antenna | |||
Electrolytic caps question | Boatanchors | |||
Electrolytic caps question | Boatanchors | |||
Trap end caps | Antenna | |||
Resistance Checking | Boatanchors |