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 Post subject: Zenith 8S463 rebuild
PostPosted: Nov Fri 15, 2019 11:37 pm 
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Joined: Mar Sun 30, 2014 2:27 am
Posts: 20
I started the rebuild of my 8S463 last year and set it aside for the summer. I'm pretty close to being done with it. I installed the 1629 tuning eye tube and it doesn't adjust very much. I talked to my local radio guy and he said that it's connected to the AGC circuit and probably isn't getting enough signal through to it. I get a few AM stations, but not as many as I should.


Any tips on how to trouble shoot it?

Thanks[/b]


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 Post subject: Re: Zenith 8S463 rebuild
PostPosted: Nov Sat 16, 2019 1:13 am 
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Joined: Jul Sun 26, 2015 11:34 pm
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Location: Hurdle Mills, North Carolina
Did you replace the 1 meg resistor in the eye cable and check R8 to make sure it is a meg ohm as well.

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 Post subject: Re: Zenith 8S463 rebuild
PostPosted: Nov Sat 16, 2019 2:32 am 
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Joined: Nov Mon 06, 2017 7:45 pm
Posts: 562
Location: Sherwood, Oregon
The schematic shows the eye tube should be a 6U5, not a 1629.
http://www.nostalgiaair.org/Resources/455/M0025455.htm


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 Post subject: Re: Zenith 8S463 rebuild
PostPosted: Nov Sat 16, 2019 2:27 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Beaver Falls, PA. USA
The 1629 has a 12 volt filament. A voltage doubler will be needed to use it in place of the 6U5, and the socket will need to be changed to an octal.

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 Post subject: Re: Zenith 8S463 rebuild
PostPosted: Nov Sun 17, 2019 2:44 am 
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Joined: Mar Sun 30, 2014 2:27 am
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The 1629 I bought had the voltage doubler built in the socket. The local radio guy sells them this way.

I did find a 47K resistor that was reading 600 ohms. I replaced that and I get more stations but the tube is not working properly.


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 Post subject: Re: Zenith 8S463 rebuild
PostPosted: Nov Sun 17, 2019 12:56 pm 
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Joined: Jun Sun 03, 2012 12:40 am
Posts: 1325
Location: Cromwell, Connecticut
A couple of things that will help us help you.

First, what have you done to the radio other than replacing the 47K resistor and the eye tube?

What test equipment do you have? A volt meter and a signal generator are the most useful here. If you don’t have access to a tube tester, spare tubes are helpful.

Your radio guy is correct, it sounds like you don’t have enough signal, as this radio with its built in loop antenna really pulls in stations. You may be in an area where there aren’t many stations and this would be good to know too. I agree that the 1 Meg resistor in the eye tube socket should be replaced.

Some of the causes are weak tubes, bad paper and filter caps, out of tolerance resistors, not using the wavemagnet antenna when testing the radio, and need of alignment. Often the 1232/7G7 RF tube is weak or has a dirty socket.

Voltage readings at various points is helpful. Riders has a page separate from the Schematic that provides this. I’ll see if I can find it.

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People may not remember how fast you did a job, but they will remember how well you did it.


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 Post subject: Re: Zenith 8S463 rebuild
PostPosted: Nov Sun 17, 2019 1:52 pm 
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Joined: Jun Sun 03, 2012 12:40 am
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Location: Cromwell, Connecticut
https://www.americanradiohistory.com/Archive-Rider/41/Rider-1941-VWXYZ.pdf

Here is the section on voltages. Go to page 196


Attachments:
Zenith 5808.JPG
Zenith 5808.JPG [ 220.58 KiB | Viewed 266 times ]

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Tony

People may not remember how fast you did a job, but they will remember how well you did it.
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 Post subject: Re: Zenith 8S463 rebuild
PostPosted: Nov Sun 17, 2019 4:16 pm 
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Location: Detroit, MI USA
If anything, the 1629 will close a lot faster than the 6U5 would have in a properly working set, since it has a spec closer to that of the 6E5. Therefore, it proves there is something wrong with either the circuit or the alignment.

Can we presume you are using the correct wavemagnet antenna that belongs to this chassis? As Tony mentioned, that's very critical for proper operation.

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Dennis

Experience is what you gain when the results aren't what you were expecting.


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 Post subject: Re: Zenith 8S463 rebuild
PostPosted: Nov Sun 17, 2019 5:27 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 9348
Location: Beaver Falls, PA. USA
There is a local-distant switch on the Wavemagnet; it will reduce the sensitivity if it is in the local position. Make sure that the plate choke of the 1232 is not open.

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