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 Post subject: Zenith H723 Questions
PostPosted: Aug Thu 25, 2005 7:34 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 37
Location: Arlington, Texas, USA
I wanted an old AM/FM radio for my desk at work so I bought a Zenith H723 on eBay. When it arrived, the right side of the case was smashed. <P>I was able to glue the pieces back togeather and polish the cabinet. I redyed the grill cloth and painted the dial pointer. Now that the cabinet is done, I am starting on the chassis. It is in Ryder's page 23-7.<P>The radio played on AM, but not on FM. Also, as soon as the radio was plugged in the power came on. The power problem was traced to a shorted AC bypass capacitor C26. The lower half of the dual capacitor was shorted to ground bypassing the power switch. The FM started working after cleaning the band selector switch. <P>I am in the process of re-capping this set, but I have a few questions. First, does this set suffer from the Silver/Mica cap problem? After about an hour of use it develops a low level buzz that does not vary with volume or tuning.<P>Second, this set has a 12BA6 in place of the 6BJ6 tube in the IF. Should I leave it there or replace it with a 6BJ6 as the schematic shows? The current tube line up is: 12BA6 IF, 12AT7 converter, 6BJ6 1ST IF, 12BA6 2ND IF, 12AU6 Limiter, 19T8 Descriminator, 35C5 Power Amp.<P>Thanks for any help.<P>------------------<BR>


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 Post subject: Zenith H723 Questions
PostPosted: Aug Thu 25, 2005 2:58 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1944
Location: OOLTEWAH,TN.
Have you changed the elec.capacitors if not i would and yes it can have have siver/mica problem but i don't think your does the vol.does not control it on your set yours is a buzz is the 12BA6 original zenith if not i would go with a 6BJ6 also the output tube 35C5 may be bad hope some of this helps not a bad radio have one somewhere SMITHY <P>------------------<BR>


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 Post subject: Zenith H723 Questions
PostPosted: Aug Thu 25, 2005 6:14 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4229
Location: Rochester NY USA
There are versions of the 723/724 using 12BA6, which is interchangeable anyway in a series set... I'd leave it. Were the electrolytics changed yet? The 19T8 could have H-K leakage, or the 35C5.<P>------------------<BR>


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 Post subject: Zenith H723 Questions
PostPosted: Aug Thu 25, 2005 6:20 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3176
Location: California
I have restored at least a dozen of this chassis, and not one has ever shown any signs of the silver migration disease. That is not to say they may not someday, but so far, none of them has.<P>Check all your tubes for any leakage. This is going to be a little tough, because you will have to run the radio until it develops the hum, then yank a tube (I would start with that 35C5) and put it in the tester really quick before it cools off. Test each tube for ANY leakage and replace if found leaky. <P>All this assumes you have already replaced the Electrolytic cap. It is a 2-section cap. I have also found a bad rectifier diode in one radio that caused hum.<P>When you are done, you will have one super hot performing radio that sounds real nice!<P>------------------<BR>DISCLAIMER: The above post is the opinion of the poster and is not intended as a political, religious, racial or gender slur. If you take offense to the above post, it is not the fault of the poster, but the fault of the reader alone. The information included in the above post was provided free of charge and without warranty. Read at your own risk.


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