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Old 19th June 2007, 03:53 AM   #1
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Default First Recap Question

Hi again guys,

Okay, I'm going to start my first recap of a mid 60's Motorola am radio.

From the schematic the radio calls for these caps:

2- 500uF/16v
1-10uF/25v
1-10uF/64v
1-1.6uF/25v

The one's that I have are as follows:

2-500uF/50v
1-100uF/50v
1-25uF/25v
1-2.2/50v

Will these work as substitutes (I hope)?

I also have the following just in case:

2-1000uF/25v
1-250uF/50v

I don't want to put the wrong values in and have problems so I'm putting it to you experts I know there is a range variance and leeway here.

Any help would be appreciated.

Thanks !
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Old 19th June 2007, 08:38 AM   #2
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Default Re: First Recap Question

Hi,

You should stick to the original values until you know a bit more about their function in the circuit. The originals were chosen for a reason and you may end up with a non-working radio if you deviate from original spec.!

Your instincts are right. Some values can be more flexible than others but do you know which? I sure don't either!

The most important things to remember about caps:

Always check the polarity/orientation of electrolytic caps.
Always replace caps with the same or greater voltage ratings. You may end up seeing some smoke if these rules aren't followed.

Your 500uF caps are suitable because they are the same capacity and rated for a higher voltage. They might be physically larger though but you should be OK given the age of the original parts (probably large anyway).

Bottom line: Splash out on the proper parts and you will have a working radio for years to come.

Good luck,
Martin.
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Old 19th June 2007, 08:45 AM   #3
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Yes I think only one or two of your proposed replacements are suitable. It's OK to have more voltage, but the capacitance must always be the same.

Also, I'm a believer in if it aint broke don't fix it. I've plenty of ancient stuff that works fine and has been untouched since it was made. Is the radio showing signs of age in terms of it's performance?
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Old 19th June 2007, 12:39 PM   #4
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Hi again guys and thank you for your advice. I appreciate it.
My understanding is that capacitance can be 20% lower and up to 100% greater than the specified value? I hear you on the voltage rating though. Don't want to go too low on that!
The 2.2uF/50v should work in replacement of the 1.6uF/25v shouldn't it?

Do the arrows on the caps indicate the + side ? The originals have a band designating + so I'm assuming (uh oh) that the arrows have replaced the "bands".

Any recommendations on a good supplier of caps?

The radio powers up but I only get static up and down the dial. I don't see that any of the original caps have leaked but have learned that leakage doesn't necessarily mean that the cap isn't dry inside.

Thanks once again,
Steve
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Old 19th June 2007, 01:03 PM   #5
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Capacitance tolerance can be quite wide, but I'd still try and stick to original values. They aren't hard to find. Banding usually indicates negative.

If you are only getting static I would guess the caps aren't going to help, they will be mainly for the audio output side of things, which seems to be working fine. My guess is a problem with the tuning circuitry or aerial.
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Old 19th June 2007, 02:07 PM   #6
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I suggest using 105C rated caps, and match the capacitance the best you can. In power supply circuits, you can usually go up a little bit, but don't double it or anything like that.

I also suggest putting in the highest voltage rating you can physically fit. Higher voltage ratings means higher ripple current capability, and longer life. Lower ESR, too.
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Old 19th June 2007, 05:30 PM   #7
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I'm using 85 C caps. Those should be okay?

For the 1-10uF/25v and 1-10uF/64v caps would it be okay to use 10uF/160v? If so I have those also.
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Old 19th June 2007, 06:53 PM   #8
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Quote:
I'm using 85 C caps. Those should be okay?
Sure. In environments where there is lots of heat, it's just better to use 105C.

Quote:
For the 1-10uF/25v and 1-10uF/64v caps would it be okay to use 10uF/160v?
Absolutely. Anything equal or greater in voltage is good. More voltage, the better (at least in power supply circuits, and IMO coupling too). What is more important is that you are equal or close in uF rating. Unless you know the circuit well, keep those the same.
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Old 19th June 2007, 07:52 PM   #9
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Quote:
Originally posted by zigzagflux

Sure. In environments where there is lots of heat, it's just better to use 105C.



Absolutely. Anything equal or greater in voltage is good. More voltage, the better (at least in power supply circuits, and IMO coupling too). What is more important is that you are equal or close in uF rating. Unless you know the circuit well, keep those the same.
Thanks Zig,

So is it safe to say that with the given values of the caps I have it's a go for starting my recap?
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Old 19th June 2007, 07:54 PM   #10
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I'll take your advice on the heat ratings on my next run too
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