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Zenith C725 help! - Printable Version

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Zenith C725 help! - TheUniversalDave1 - 03-07-2016

I got this radio at an estate sale a few weeks ago, and I have become very fond of it. It has (had) a very clear, excellent sound. But tonight, I was listening to it, and all at once, it went completely silent. I clicked it off, and I heard a ten second long buzz that slowly faded away. The first thing I thought was that the selenium rectifier had shorted. Any ideas? I really like this radio - I just got finished giving it the Novus treatment and the cabinet is in near mint condition.

RE: Zenith C725 help! - Radioroslyn - 03-07-2016

Hi Dave,
You'll find the service info here: http://www.rsp-italy.it/Electronics/Radio%20Schematics/Collections/Beitman/1960.pdf
on page 174.
Check the dc voltage at the + side of the rectifier should see 100v or better.

Terry

RE: Zenith C725 help! - TV MAN - 03-07-2016

These radios were good performers. I have several including one I got as a youngster. It played and played and played. I haven't had it on for years, and probably wont until it gets recapped. Speaking of which, if your radio hasn't been recapped, it could be one of the capacitors shorted. Like Terry said, check for B+ off the rectifier to chassis ground. Likely one of the filter caps gave it up and shorted. I do know from experience that the am/fm band switches are a little finicky on these and can cut out. I don't think the selenium rectifier would have shorted. I don't recall these doing this, usually they get weak and B+ is low. Sometimes they get hot and have a nasty smell. They don't last forever. Oh, do the tubes light? This is a series strung set, so if one tube heater opens up, set will go dead. These are just a few things to check for starters.

RE: Zenith C725 help! - TheUniversalDave1 - 03-07-2016

I've been told on another forum that the 19T8 and the 35C5 are troble probe and they could have developed a heater to cathode short. I hope it's something that simple. I will be recapping this radio as soon as possible.

RE: Zenith C725 help! - David - 03-07-2016

When recapping if it was my radio I would replace the selenium diode. You will need to change the value of the 22 ohm resistor (R3?) to something around 50 ohms then check voltage and adjust. I have had good luck with 19T8 and 35C5 tubes in Z sets. Glad to see your set has a 12AT7  instead of 12DT8 that is the tube I have the most problems with in Z sets. Give the slide switch a good cleaning. Good Luck David

RE: Zenith C725 help! - TheUniversalDave1 - 03-07-2016

Thanks for the information

One thing that irritates me is when people say "Brand Z" as if Zenith is a word of profanity.
Zenith
zEnith
zeNith
zenIth
zeniTh
zenitH

RE: Zenith C725 help! - doc612 - 03-09-2016

You're a weirdo, sir! Hey, bring the ZENITH to the club Saturday and we'll play with it okay? See ya,
Doc

RE: Zenith C725 help! - TheUniversalDave1 - 03-10-2016

I found the problem, Doc. One of the 12BA6's was shot. I popped a new one in and it sounds great. I won't be able to go to the shop this Saturday. I'm riding with Gene to Atlanta.

RE: Zenith C725 help! - TV MAN - 03-11-2016

Yep, tubes still go bad like in the old days. Glad you found the culprit! Icon_clap