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Old 11th March 2012, 09:09 PM   #1
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Default Newb - need help identifying caps

Hope I put this in the right area.

After months of procrastination, I have finally started my "winter" project: recapping my grandpa's 60's Zenith tube stereo (MLT-15). I found the schematics on Sam's and the tuner diagram is awesome, but the amp diagram is a little different than mine (the amp on the schemo is on the same chassis, but has an extra tube and the guts are different).

Long story short, I can't go by the diagrams to figure out the values of all the caps in the amp, and I'm basically brand new to DIY electronics. I have about 5 caps that I'm having a hard time with - they all have colored bands to indicate values. I found this, but I'm still second guessing what I'm coming up with.

Any words of wisdom on figuring these out? I can post pictures if it would help, but I would like to figure out how to read these rather than just having you guys tell me what they all are.

Thanks a bunch. I know I'll be around here a lot over the next few months as I figure this out.
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Old 11th March 2012, 10:32 PM   #2
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Yeah, I'm familiar with some of those "winter projects" that get started about the time the smelt runs start.

Going by memory, I think those are paper-and-foil, or perhaps early plastic film, capacitors. If that recollection is correct, I'd be inclined to measure leakage and dissipation before I assumed they required replacement. (On the other hand, a modern film capacitor might provide some improvement over the equipment's original performance.)

There may have been more than one system for color-coding the values. A copy of the ARRL "Radio Amateur's Handbook" from the 50's or 60's may have the information you need to read the code. (Ask at your library - it may be on microfilm or computer file). Yes, a good photo may help but correctly identifying colors that may have faded over time is another matter.

I've probably told you more than I know but I hope it helps.

Dale
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Old 12th March 2012, 11:02 AM   #3
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Thanks for the help. It seems everywhere on the 'net that I look, people say to rip all the old non-ceramic caps out of these things and replace them as long as I have the chassis pulled. I will definitely be replacing the the electrolytic caps, but it would save me a lot of headache if I didn't have to swap all the others, too. I will post photos this evening.
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Old 13th March 2012, 01:42 AM   #4
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Here's a closeup of one of the caps - let me know if you have any thoughts.
Attached Images
File Type: jpg cap.jpg (50.1 KB, 74 views)
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Old 13th March 2012, 03:39 AM   #5
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Using the diagram you posted previously, I see 0.033 uF (33,000 pF), +/-10%, 200 V.

A polyester film capacitor rated for 0.033 uF, at 250 V (or higher) should cost roughly $0.50, and be easily obtained.

Dale
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Old 13th March 2012, 05:35 AM   #6
nazaroo is offline nazaroo  Canada
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Quote:
Originally Posted by rave0035 View Post
Here's a closeup of one of the caps - let me know if you have any thoughts.
that object with the color bands is a resistor.

The disk cap to the right should have specs or a part # right on it.
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Old 13th March 2012, 11:51 AM   #7
godfrey is online now godfrey  South Africa
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I doubt it's a resistor. That color code would make it 333 Gigohm.
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Old 13th March 2012, 11:15 PM   #8
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Quote:
Originally Posted by dchisholm View Post
Using the diagram you posted previously, I see 0.033 uF (33,000 pF), +/-10%, 200 V.
Dale
Thanks for the help Dale, I just wanted confirmation that I was reading these correctly. On a related note, it's acceptable to exceed the V rating of the initial cap if I can't match the original?
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Old 13th March 2012, 11:17 PM   #9
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Quote:
Originally Posted by nazaroo View Post
that object with the color bands is a resistor.
The resistors in this unit look similar, but are brown (rather than black).
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Old 13th March 2012, 11:20 PM   #10
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Quote:
Originally Posted by rave0035 View Post

Long story short, I can't go by the diagrams to figure out the values of all the caps in the amp, and I'm basically brand new to DIY electronics.
Why not buy an LCR meter ?
Much better than guessing.

Take one out at a time, measure it then replace it with a new one.
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