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Zenith L721 bumble bee cap.

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Zenith L721 bumble bee cap. Empty Zenith L721 bumble bee cap.

Post by terrydec on Wed Mar 15, 2017 2:07 pm

I had this great sounding Zenith L721 AM/FM radio. I gave it to a friend and it played great for awhile. Then it went zzzzpt and quit. He sent it back and when I opened it up I found a bumble bee cap had exploded. It comes from pin 3 of the output tube to ground, and of course I can't find it on the schematic. The markings are-
yellow, violet, orange, black, yellow. My guess is .047 mfd. What I really need to find out is why it exploded in the first place. I also need to replace the filter caps. Whooppee! Some fun, huh?
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Post by terrydec on Wed Mar 15, 2017 3:16 pm

I figured it out. It's 470mmf. I got nuttin' like that. That would be a mica, right? Would a regular orange drop work? All I got are used electrolytics. It looks like an order to ARS.
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Post by easyrider8 on Wed Mar 15, 2017 5:22 pm

From pin #3 of the 35C5 to ground would be a .047 capacitor. Bumble bees in that position (across the line) are notorious for failing in that fashion. You would want to replace it with a "X" rated safety capacitor.

Dave
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Post by terrydec on Wed Mar 15, 2017 6:29 pm

Okay- I'm dumb. What is that and where do I get one?
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Post by easyrider8 on Wed Mar 15, 2017 8:14 pm

Send me a private message with your snail mail address and I will send you one.

Here is the info. http://www.kemet.com/Lists/Filestore/EvoxRifaRFIandSMD.pdf

Dave
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Post by mafiamen2 on Thu Mar 16, 2017 1:43 pm

great info dave thanks

sam
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Post by terrydec on Thu Mar 16, 2017 2:42 pm

Yep!

Isn't this forum the best?

I think this one shorted. Would that take out the filter cap? This set played perfectly when I sent it out. Now it has hum and the signal is distorted.
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Post by terrydec on Thu Mar 16, 2017 2:45 pm

BTW- This set has a chassis ground. Dangerous. Good thing I have an isolation transformer. However replacing the filters will be a real challenge.
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Post by Bill Cahill on Thu Mar 16, 2017 5:47 pm

No, but, there's a good chance it took out one, or, more tube filaments. Pin 3 is one of the filament pins.

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Post by terrydec on Thu Mar 16, 2017 6:28 pm

Bill Cahill wrote:No, but, there's a good chance it took out one, or, more tube filaments. Pin 3 is one of the filament pins.

It works, so the tubes are okay. The 30C5 was a little weak so I replaced it. I never worked on this radio because it played. I got it for the FM. Then I sold it to a friend. It worked great, but now it is distorted and hums. My friend says it made a funny noise, started to hum and stopped working. Is it possible that one of the electrolytic caps shorted? What about the Selenium rectifier? At least it still does pass a signal.
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Post by Bill Cahill on Thu Mar 16, 2017 6:52 pm

Could be, but, I'd replace that paper capacitor, first.

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Post by terrydec on Thu Mar 16, 2017 10:54 pm

I'm gonna replace that cap and the electrolytics. Then I intend to bring the power up VERY slowly and see what I have then. I hate poking around in FM sets. I barely understand AM. And this has a hot chassis.

BTW- Thanks for all your responses.
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