| Zero Cool |
I am repairing my HP651B Oscillator. It is getting to that age where the caps are going bad.
The output is fed through a 1200uf 10VNP cap. which i assume the VNP stands for Volts, Non Polarized.
My Fluke 189 shows the value of the cap to be good but i suspect its age is causing some problems. I get some DC offset occasionally.
So two questions. where to get a BIG NP cap as such.
and two, what factors should i look for in a NP cap. I would like to replace it with an equivalent or better part.
Could i use a couple of caps back to back to form the NP??? and what issues would i face as such? |
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| dave_gerecke |
Hello ZeroCool, Your best bet for large value NP electrolytics is probably someone like Madisound, Parts Express, Zalytron, etc. Look for companies that specialize in supplying DIY speaker builders. I took a quick look at Madisound and the had some from Bennic that went to 1000 uF. This one possibility. If you are really trying for exact value, parallel a 200uF with it.
You can also put two conventional electrolytics back to back to get the same effect. Issues I can think of quickly are space contstraints.
Peace,
Dave |
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| Zero Cool |
| I have plenty of space in this unit. so thats not an issue. Just want to make sure i can repair it as best as possible. I use this thing every day! |
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| dave_gerecke |
I can understand. From what I saw with a little quick looking around, Madisound seemed to have the largest available NP Electrolytic at 1000uF. Parts Express stopped at 500uF and Zalytron didn't appear to carry NP Electro's at all. I would say do a price comparison between Madisound and Parts Express, and also compare for quality where possible. Then buy the ones you need to put a few in parallel to get the 1200uF value you need. The caps for the crossovers that were listed at both sites are rated for 100v, so they should have no problem in your application.
Peace,
Dave
P.S. Please report back on your success!:) |
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| Zero Cool |
When putting two caps in series back to back to form a Bi-Polar/Non polar whatever you want to call it. Is the capacitance still added? or will the value be that of each individual capacitor?
IE: if i put two 600uf caps together in series. do i have 1200uf or 600uf??
Connecting them + to - i would assume it would be 1200uf. But because they are back to back, is it then the same???
And, does it matter if i connect them +to+ or -to-???
Zc |
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| dave_gerecke |
Hello Zero Cool, I am having a bit of a mental block in regards to what the capacitance value will be, I think it will stay the same as the value of one of the caps, but to make a Bi-polar cap, you would hook the positive leads of both caps together, with the caps in series. Then the negative terminals become the connections to the rest of the circuit.
If you want a larger value of capacitance, you would hook the caps in parallel. If you want a smaller value of capacitance, but a higher voltage capability, you would hook the caps in series.
Caps in parallel are additive, caps in series are subtractive. But series wiring of caps increases the voltage capability. The subtraction only happens if you hook positive to negative. If you do this to increase the voltage, use caps that are rated at the same voltage and capacitance value, and put large value resistors in parallel with each cap. The resistors will help balance the load between the two (or more) caps.
Hope this helps.
Peace,
Dave |
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| DigitalJunkie |
Connecting the caps in series will yield half the capacitance,will it not?
So,for 1200uf,you'd need 2x 2400uf caps back-to-back. :confused: |
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| jcx |
nonpolar (aka Bi-polar) Al electros measure lower distortion than back to back series normal polar electrolytics
higher V rating performs better too
if blocking Volts of DC then series nonpolar Al electros were the best high value type in Bateman's tests
search digikey - panasonic SU Bi-polar 2200uF 25V in stock
http://search.digikey.com/scripts/D...l?name=P1185-ND |
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| Zero Cool |
| I wonder if a larger value in this instance would hurt performance any??? The Osc goes quite low in Freq. less then 1 hz i think so thats why they used such a large NP in the first place. I wonder if using a bigger NP will hurt any?? |
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| jackinnj |
| NP has recommended the ELNA "Silk" caps for the F4 -- so I would suspect that RFS35V102MK8 (604-1069-ND from DK's website (1000u/35V) would fit the bill). |
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| Zero Cool |
| quote: | Originally posted by jackinnj
NP has recommended the ELNA "Silk" caps for the F4 -- so I would suspect that RFS35V102MK8 (604-1069-ND from DK's website (1000u/35V) would fit the bill). |
Those are polarized however as far as i can tell. But maybe a couple of those back to back |
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| jackinnj |
The ELNA silks are a pretty remarkable capacitor -- Digikey has them back in stock --
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| Zero Cool |
Digging through some boxes i found some NOS 4 lead Sprauge 2200uf 63v N.P or BP caps. took me a little while to figure them out. each end has 2 leads coming out. seems each respective lead is carried through to the other side. I was able to clip one lead off per side and get it installed.
I don't know if the distortion is any better or worse now. but there is little measurable DC offset at 10hz or at 10mhz So i will give it a try for a bit and keep looking for a good replacement N.P cap. just in case.
Zc |
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