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Thread: Weird Capacitors! Need help determining replacement value

  1. #1
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    Weird Capacitors! Need help determining replacement value

    So I've never seen capacitors like this before, in fact I'm not even 100% sure they ARE caps. They're referenced as C on the circuit board along with some other known capacitors though, so I'm to believe they are capacitors. Unfortunately none of them measure any capacitance on my multimeter and I can't understand the markings to determine replacement values. I also can't find a schematic for this amp (Carlsboro solid state amp).

    Here's a picture:

    dsc01186.jpg

    The values written on the capacitors are like "100 MN". Any ideas?

  2. #2
    Supporting Member mozz's Avatar
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    Do they measure any resistance? Model number? Problem you are encountering? If they are caps, I can't believe that many would be open, test known good caps with your meter, start at 100pf.

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    Quote Originally Posted by mozz View Post
    Do they measure any resistance? Model number? Problem you are encountering? If they are caps, I can't believe that many would be open, test known good caps with your meter, start at 100pf.
    Known good caps measure accurately. These mystery "Caps" all measure OPEN for resistance. This amplifier was making a lot of noise (windy, popping, etc..) and I replaced all of the electrolytic capacitors - it's quieted down but I'm still getting some Popping. The popping isn't affected by the channel volumes or tone controls, but it does go away when the Master vol is turned down.

  4. #4
    Supporting Member Jazz P Bass's Avatar
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    Measuring a small value capacitor with your meter set to read resistance is pointless.

    Most caps will read open circuit.
    Electrolytic caps will show a reading as the meter voltage charges them up but this is not a valid test of the cap.

    If nothing else, go out and purchase a cheap meter that has a capacitance tester.
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  5. #5
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    I recognise those as caps, though can't recall the technology.
    The numbers are probably their value in pF

  6. #6
    Senior Member Enzo's Avatar
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    They look like common ceramic caps to me. Common in a previous era, yes, but tube TV sets would be full of them. Numbers ought to be cap value in picofards.
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    Quote Originally Posted by Jazz P Bass View Post
    Measuring a small value capacitor with your meter set to read resistance is pointless.

    Most caps will read open circuit.
    Electrolytic caps will show a reading as the meter voltage charges them up but this is not a valid test of the cap.

    If nothing else, go out and purchase a cheap meter that has a capacitance tester.
    Hey JPB, I was measuring them in the capacitance setting but was responding to mozz who asked what they measured in resistance (presumably to see if they're something other than capacitors).

  8. #8
    Supporting Member mozz's Avatar
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    I just mentioned resistance because he wasn't 100% sure they were actually a cap. If they are pf caps, why no meter reading? M could be tolerance 20% and then N stands for nano? Still doesn't answer why would they all be open. How old of a solid state amp? 1965? 1985?

    Here are some tube schematics, other page shows some of those caps even on the tube amp models, schematics call them 3kpf, 47kpf.

    Carlsbro Amplifier Vintage Wiring Diagrams
    Servicing a Carlsbro CS100 Reverb PA Amplifier

    carl17c.jpg
    Last edited by mozz; 09-02-2017 at 11:43 PM.
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    Wonder if MN is milli-nano, which would be pico
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    rjb
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    Quote Originally Posted by glebert View Post
    Wonder if MN is milli-nano, which would be pico
    Unless kpf is kilo-picofarad, which would be nanofarad.

  11. #11
    g1
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    Does your meter cap setting normally measure down to small values like 50pF ?
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  12. #12
    Senior Member Enzo's Avatar
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    milli-nano??? Now I have heard everything.
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  13. #13
    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by Enzo View Post
    milli-nano??? Now I have heard everything.
    No Sir, you still need to listen to milli-vanilli

    enjoy specially from 0:52 on
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    Juan Manuel Fahey

  14. #14
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    MV... great, now my Master Volume knobs on my amps (built or bought) will be called the "Milli-Vanilli" knob. Because Milli-Vanilli and Master Volumes are equally criminal inventions foisted upon the world.

    Juan, that was as horrible as it was 30 years ago when I had to hear it on the school bus. A pox on you for posting that! T-Boy, where's that "HULK SMASH!" button?

    Justin
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    "Are you practicing in the lobby of the municipal library? It's still a guitar amp and it SHOULD make some noise (!!!)" - Chuck H. -
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  15. #15
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    Ok, hereīs the antibiotics to cure that ear infection

    Juan Manuel Fahey

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    Quote Originally Posted by waspclothes View Post
    Hey JPB, I was measuring them in the capacitance setting but was responding to mozz who asked what they measured in resistance (presumably to see if they're something other than capacitors).
    Most multimeters won't give you any accuracy at all under maybe a few hundred pf of capacitance. I think there are many techs who would argue that testing capacitance on almost all multimeters to be a convenient approximation at best, and any reliable reading should be done on a calibrated instrument (and probably at the high end of its voltage rating).

    edit: I think these are vintage "dogbone" temperature compensating type ceramic capacitors. "MN" might be the tolerance or something.
    Last edited by SoulFetish; 09-03-2017 at 07:02 AM.
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  17. #17
    Old Timer Tom Phillips's Avatar
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    I'm wondering, during this whole thread, why all those parts were removed in the first place. I.e what troubleshooting pointed to them as "bad?"
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  18. #18
    Senior Member Pedro Vecino's Avatar
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    Ceramic tubular capacitors. Measurements are usually in picofarads, from a few to 5000. Itīs very difficult to find them damaged.
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  19. #19
    Old Timer J M Fahey's Avatar
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    Yes, they very much look like old style (say the 50`s, 60īs) ceramic caps.
    If some factory was already set up to make them that way, they would keep doing so until dies or machines broke or wore off, they would be well amortized anyway.
    Any new production line would be set up to make them the modern way, of course.

    I read them as small value ceramics, visible value being from 33pF to 100pF, *very* hard to read on a multimeter since probably cable and test leads would already show more than 100pF.
    And if user is holding probes with his hands, forget about it.

    A proper LCR meter would have them attached to some terminals, no human hands nearby, and even so might show "parasitic" 10 to 50 pF, which would have to be substracted from displayed measurement

    I have this very same model, faithfully working since the late 70īs:


    I think the caps shown are ceramics, value in pF is the printed number, and MN either shows voltage and tolerance or temperature coefficient or is plain brand indicator (Minnesota Capacitors anybody? )
    mysterycaps.jpg
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  20. #20
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    Quote Originally Posted by Tom Phillips View Post
    I'm wondering, during this whole thread, why all those parts were removed in the first place. I.e what troubleshooting pointed to them as "bad?"
    Me too! I would list bad semiconductors, electrolytics, then resistors as noise suspects in that order for a SS amp. Little caps like those would be last.
    Experience is something you get, just after you really needed it.

  21. #21
    Old Timer J M Fahey's Avatar
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    Agree.
    Ceramic tubular capacitors, number is capacitance in pF, no need to stablish units, MN may be voltage and tolerance or temperature coefficient code, donīt expect any mystery data.
    Or even plain Brand label.
    They should never have been pulled, shotgunning is a terrible repair technique and in any case they would never cause noise as described, which is way more possible coming from bad active components, in general ICs or transistors.
    Juan Manuel Fahey

  22. #22
    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by J M Fahey View Post
    Yes, they very much look like old style (say the 50`s, 60īs) ceramic caps.
    If some factory was already set up to make them that way, they would keep doing so until dies or machines broke or wore off, they would be well amortized anyway.
    Any new production line would be set up to make them the modern way, of course.

    I read them as small value ceramics, visible value being from 33pF to 100pF, *very* hard to read on a multimeter since probably cable and test leads would already show more than 100pF.
    And if user is holding probes with his hands, forget about it.

    A proper LCR meter would have them attached to some terminals, no human hands nearby, and even so might show "parasitic" 10 to 50 pF, which would have to be substracted from displayed measurement

    I have this very same model, faithfully working since the late 70īs:
    That LCR meter is a sweet unit, Fahey! I want one of those. I admit, I have a little bit of gear envy.
    (But how obnoxious is it the i look over and see the "range multiplier" switches and think "Ew! I would have to do it?" #spoiledbyautorange)
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  23. #23
    Better Tone thru Mathematics bob p's Avatar
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    I have one of these. current production, easy to find.



    https://www.bkprecision.com/products...-with-esr.html
    Attached Thumbnails Attached Thumbnails 880_front_lrg.jpg  
    "Stand back, I'm holding a calculator." - chinrest

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    Quote Originally Posted by J M Fahey View Post
    Agree.
    Ceramic tubular capacitors, number is capacitance in pF, no need to stablish units, MN may be voltage and tolerance or temperature coefficient code, donīt expect any mystery data.
    Or even plain Brand label.
    They should never have been pulled, shotgunning is a terrible repair technique and in any case they would never cause noise as described, which is way more possible coming from bad active components, in general ICs or transistors.
    Hi JMF, point taken. I thought the shotgun replacing of the mystery capacitors would be a quick experiment before I go to replacing transistors and then IC's. I thought I was onto something when they wouldn't measure any capacitance with my multimeter (and a known .1uF cap measured fine). The transistors in this are unlabelled and I can't find a schematic, so I'm not sure how to approach that problem.
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  25. #25
    Old Timer Tom Phillips's Avatar
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    Quote Originally Posted by waspclothes View Post
    Hi JMF, point taken. I thought the shotgun replacing of the mystery capacitors would be a quick experiment before I go to replacing transistors and then IC's...
    The usual troubleshooting technique is to isolate the problem to a certain area of the circuit. Granted, that is hard to do if you don't have a schematic and are not familiar with the circuit in your amp. In post number 1 you said the equipment was a Carlsboro solid state amp. I suggest that we start by getting the complete model number and photos of the amp so the group can try to find a schematic.

    Once we know more about the circuit then we can do troubleshooting to determining if various controls affect the noises. In addition, we can do various simple things to interrupt the signal path and/or dump the signal to ground with a temporary capacitor in certain places in the circuit and observe how that affects the noises. (Caution: Don't try this until you really understand the technique) Other things are thumping, poking & prodding, freeze spray, heat gun, pot, switch & connection cleaning and detailed visual inspection. The goal is to narrow down the section of the circuit where the noise is originating and all this comes before shotgun parts replacement.

    Cheers,
    Tom
    Last edited by Tom Phillips; 09-04-2017 at 06:00 AM.
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  26. #26
    Old Timer J M Fahey's Avatar
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    Excellent advice and the way to go.

    So far we know nothing, "Carlsbro SS amplifier" covers way too much, we need some focusing.
    Post model, whatever is written on the backpanel, plus some pictures:
    front and back panels, then pull chassis out and post preamp and poweramp pictures ... weīll then ask for more

    After we get some idea of what you have, weīll suggest some tests.

    I seem to have read no controls affect noise except Master Volume?

    If so, you need to detect which is the last active section , based maybe on an Op Amp or perhaps a couple transistors, which feeds/drives that MV, I guess we wonīt be far from the suspect.

    Problem is Carlsbro was actually a very popular, widely sold and available British brand (I saw them all over the place in UK in ī86, way more than Laney, Marshall or Vox, go figure) , but since "nobody famous" used them, they are ignored today.
    HH was more famous, but also disappeared, was absorbed by Laney; another popular but obscure brand was Torque.

    Sadly Music pages, IF they remember them somewhat, that applies only to Tube circuits, but never SS.
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  27. #27
    g1
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    Quote Originally Posted by waspclothes View Post
    I thought I was onto something when they wouldn't measure any capacitance with my multimeter (and a known .1uF cap measured fine).
    This is what I was getting at. A .1uF is 100,000pF. You are trying to measure caps in the vicinity of what we think is 50pF. A lot of multi-meters with capacitance functions will not measure caps of such a low value.
    I would guess that when you measure them, you get the same reading as when the probes are open and not touching anything.
    If you were comparing to a known good 50pF cap, and the meter measured one but not the other, then you could suspect the cap.
    Out of curiosity, what is the make and model of your meter?
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    Quote Originally Posted by Pedro Vecino View Post
    Ceramic tubular capacitors.
    I remember those! Thin-walled, hollow, ceramic tubes, metallized on the inside and outside of the tube.

    This thread is giving me flashbacks to my childhood. I started tinkering with electronics when I was about 8 years old, and saw a few of these ceramic tubular capacitors (pulled from dead electronics that was already old then) during my first few years in the hobby. I haven't seen any of them in a very long time, though.

    -Gnobuddy
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    Quote Originally Posted by J M Fahey View Post
    Agree.
    Ceramic tubular capacitors, number is capacitance in pF, no need to stablish units, MN may be voltage and tolerance or temperature coefficient code, donīt expect any mystery data.
    Or even plain Brand label.
    They should never have been pulled, shotgunning is a terrible repair technique and in any case they would never cause noise as described, which is way more possible coming from bad active components, in general ICs or transistors.
    Just a quick update. I replaced all of the LM741 and CA741 op-amps and the noise is gone. Thanks everyone for their patience on this.
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  30. #30
    Old Timer J M Fahey's Avatar
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    Glad to know
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    Quote Originally Posted by J M Fahey View Post
    Glad to know
    It's news to me that opamps can become noisy like that. Intermittent crackly noise, but still functioning. Anyone know why that happens to them and what causes it?

  32. #32
    Senior Member Enzo's Avatar
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    Semiconductors are way more likely to go noisy than caps or resistors.

    If you are looking for a "cause", you likely will never find it. If you think it will be a "I did this, so that happened...", you will be disappointed. It rarely will be anything you "did". Playing real loud into it, or turning up your fuzz pedal will not affect the amp.

    On the other hand, even when you cannot feel it, there is static electric charge on everything. it is possible at some point you plugged a guitar into the amp and a static discharge went through things and damaged a semi junction. Didn't kill it, just damaged it. Like stepping on a ladder rung and cracking it, but not all the way through. The six months later, it finally goes. Now you have no way to know what happened.

    But within the IC, a defect or weak spot in the silicon could result in noise.

    Failures elsewhere could afffect them. If for example you are running 15v rails, and a power supply fault puts 25v on the op amp, that can damage it. And again, it might not show up immediately.
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