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Caps in series-good point!


 
7/15/2000 2:09 AM
T.B.
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Caps in series-good point!
Steve,  
 
Thanks for reminding us of the series caps and the can being "hot". Like two caps in series of equal value there should be about half the DC volts at the series junction. And that thin coating they apply to the can exterior can't be much protection.  
 
I personally would never mount axial type caps outside of the chassis without a housing of some type. While mounting 'lytics inside an amp I usually sleeve the cap leads with some 600 volt thhn type insulation that I strip off say 14 or 12 gauge wire.  
 
Have a great weekend everyone, T.B.
 
7/16/2000 12:47 AM
Tom L
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Re: Capacitor "House"
Does this mean that I shouldn't replace the cardboard-covered multisection caps in my Ampegs with the metal can types? Some of those sections are connected in series.  
 
--Tom
 
7/16/2000 9:52 PM
Stephen Conner
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You can use the metal can types as long as the cans are well insulated from each other and the chassis. Most metal can caps are covered in an insulating plastic heatshrink, and the high-voltage ones usually have a plastic disc covering the end of the can too.  
 
They still shouldn't be mounted sticking out he chassis, though, because the heatshrink can easily get damaged allowing you to touch the live can. That's where the dog house comes in handy.  
 
Steve C.
 
7/16/2000 10:06 PM
T.B.
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I'm glad this thread came up. I think it's all too easy to forget when putting caps in series. At least in the "house" they are mounted on insulating board and I believe there's also insulation attached to the "housing". So it appears that mounting series caps inside a chassis, it would be wise to at least lay them on some type of insulating material, either a board type or insulating "rubber type" sheets by Scotch or similar used in wire splicing. Also it might be a good idea to mark the upper cap with the word "hot" on the outside just as a reminder.  
 
I've seen that heat shrink come apart on some old caps so wouldn't personally trust that alone. Plus you wouldn't want the DC going to ground. I've got this little Univox "champ type" amp that I was going to replace the quad can cap with individual caps but got no place to mount them except outside. Then I'd have to make a housing for them, so will probably just buy the quad can.  
 
Well, take care everyone and stay safe. T.B.
 
7/17/2000 3:43 AM
Tom L
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So, what do you Ampeg guys do?
Many Ampegs (like the V-4) do not have a doghouse over the caps, and the caps are mounted outside the chassis. The Mallory FPs with the cardboard housing are no longer available.  
 
I guess you could wrap some additional insulation around the cans if they're connected in series, but I was wondering what most people do when replacing these. Or is this one reason many of these amps still have the original caps?  
 
--Tom
 
7/17/2000 12:37 PM
T.B.
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Hi Tom,  
 
I have a V-4 that I'll get around to servicing one day and I just took a look at it and noticed about three can caps in cardboard housings. Guess that's something I'll have to figure out when I get to it.  
 
Don't know if there's room inside the amp or not. Surely someone has already crossed that bridge and could fill us in.  
 
Take care, T.B.
 
7/17/2000 1:34 PM
Casey4s
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I just simply replaced mine with Mallory metal can types on my VT22 and there is no problem. The can itself is connected to the cap ground as far as I know. The caps inside are independent and are not in series. I think that was the original concern.  
 
Casey4s
 
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