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  #1  
Old 09-12-2014, 11:47 AM
quartermoonp quartermoonp is offline
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Bakelite Question

Hi,

Is this a suitable replacement for the innards on a 0.05 Mfd Bakelite Block?

http://www.mouser.com/ProductDetail/...n1p2vhg7KKs%3d

Thanks!
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Old 09-12-2014, 02:24 PM
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Yes unless the AC line connects to it. Then you should use a safety cap. More info on that here: http://www.justradios.com/safetytips.html
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Old 09-12-2014, 03:33 PM
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If the original is rated at 630volts or less then your good. As a general rule in radios a 10-20% tolerance in capacitance value is just fine.

What kind of bakelite block is it? The Philco block-caps that bolted to the chassis often had two caps and maybe some resistors inside, so you would need to look up the part number and verify the contents before ordering replacement parts...And if it is across the power cord then you should get AC rated replacements.

Are you planning to restuff it? Philco blocks I recommend restuffing, but other types would have to be installed in a DARN expensive/rare set for me to think about it.
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Old 09-12-2014, 03:38 PM
quartermoonp quartermoonp is offline
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These are the Philco Block caps -the chassis is Model 665 for schematic reference.
I looked at the Philco repair bench to determine what each bakelite contains, but I'm glad you said something. Plus I cross referenced with the schematic to make sure the part numbers line up.
I'm going to re-stuff these. I need to see if any of these are across the power cord - but any help is greatly appreciated.

for the Mica's, Is it better to replace these caps as well?
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Old 09-12-2014, 04:00 PM
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Genuine micas (not those 'micamold' paper caps) tend to still be in good working shape in tube radios, and thus don't need to be touched.

Here is a tip on rebuilding block caps. Once you remove them use a flat edge screwdriver to chip out the tar and old parts out from the underneath...The black tar at least (I hear there were other kinds) is fairly soft and easy to chip out, and it is a lot less hullabaloo than using heat to melt the tar loose.

If there are any across the power cord it likely will be obvious as IIRC Philco liked to use them as the connection lugs for the power cord.If it is a transformer powered set then tracing it should be a snap. The schematic will also probably show caps across the power cord if they are used in your set.
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Old 09-12-2014, 06:47 PM
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I just checked the 665 and schematic and cap 91 is the one to watch out for. It has two 0.015 uF caps inside. Each going to one side of the AC line and ground. Make sure to use "Y" type safety caps there or just leave it out if you don't have any handy. They are there to filter out line noise and the radio will work without them.
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Old 09-13-2014, 05:28 PM
quartermoonp quartermoonp is offline
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Quote:
Originally Posted by bandersen View Post
I just checked the 665 and schematic and cap 91 is the one to watch out for. It has two 0.015 uF caps inside. Each going to one side of the AC line and ground. Make sure to use "Y" type safety caps there or just leave it out if you don't have any handy. They are there to filter out line noise and the radio will work without them.
Thanks Bandersen!
My background is restoring solid state receivers, amps, reel to reel, etc. Having said that, doing this new to me project is definitely an exploration into a new world. As in the solid state world, small value capacitors end up being either ceramic disc or metal film. So for say a 0.1uf cap, this always ends up being a film - usually polypropelene - capacitor. I take it that it's fine to use these for the small value caps?

I'm finding this chassis pretty challenging because someone at some point has been inside this chassis and already bypassed the original metal can Caps, including the multi section one. So far, I've been able to get the values on these, although there's been some leakage from the original caps (big surprise). Some of the leakage has reached the replacement caps, so as I said before, it's been a bit of a challenge reading some of these.
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Old 09-14-2014, 02:33 PM
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Yes, polypropylene or polyester film caps are perfect for replacing the old caps.
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Old 09-15-2014, 11:06 AM
quartermoonp quartermoonp is offline
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Quote:
Originally Posted by bandersen View Post
I just checked the 665 and schematic and cap 91 is the one to watch out for. It has two 0.015 uF caps inside. Each going to one side of the AC line and ground. Make sure to use "Y" type safety caps there or just leave it out if you don't have any handy. They are there to filter out line noise and the radio will work without them.
Would this work fine for this?
http://www.mouser.com/ProductDetail/...noGvHf0w%3d%3d

Or is this the better choice?
http://www.mouser.com/ProductDetail/...EDFd%2fWdMU%3d

thanks,

Last edited by quartermoonp; 09-15-2014 at 11:12 AM.
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Old 09-15-2014, 12:10 PM
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Use the first one: http://www.mouser.com/ProductDetail/...noGvHf0w%3d%3d

It's rated as Y2 class That's from either leg of AC to ground.

The second one linked is only X class which is across the AC line.
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Old 09-15-2014, 12:15 PM
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Just noticed the steep price - $5.92!

Go with these instead for $1.59
http://www.mouser.com/ProductDetail/...xzFTBX3vjdk%3d
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  #12  
Old 09-16-2014, 10:36 AM
quartermoonp quartermoonp is offline
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Another Cao Question

For the 30-4024 caps (2 of them) the spec says 0.006 /1Kv

Before I realized that these carry 1000 volts, I was going with 0.006 / 630V
Now I'm thinking I should go with 0.005 / 1Kv.

Which is the correct choice?
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  #13  
Old 09-16-2014, 03:19 PM
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Always go with the same or higher voltage. The voltage rating on a cap is the max input voltage they can take before going BANG(!), and it has always cost money to raise that voltage in any given cap...So if the original designers chose a higher value than normal it was usually for a GOOD reason.

If my math is right the .005 should be within 20% tolerance, and work fine. Honestly most radio circuits can still function with the paper caps replaced by ones an entire order of magnitude or more (x10 or /10) off on capacitance value, albeit a good portion of cases show significant changes in performance and audio quality (and not always for the worst).
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