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 Post subject: TO H500 Schematic
PostPosted: Jun Mon 14, 2010 9:52 pm 
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I am restoring a Zenith TO H500 radio. I have been replacing the electrolytics and was using the schematic that came with the radio. I identified which contacts on the can were which using this schematic and removed and labelled the contections accordingly. Recently I obtained the SAMS Photofact for the H500. I noticed on this schematic the locations of the 20mF and 40mF caps seem to be switched. My question is, does anyone know which schematic is correct. Thanks


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PostPosted: Jun Mon 14, 2010 10:18 pm 
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this should help you its froim a very reliable website

http://www.transoceanic.nostalgiaair.org/h-500.htm

the website

http://www.transoceanic.nostalgiaair.org/

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 Post subject:
PostPosted: Jun Mon 14, 2010 10:36 pm 
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There are at least three variations of the chassis in the ZTO H500. The early chassis has a 2-prong headset plug on the back. The later one had an RCA phono type jack. The third used a 1U5 tube instead of a 1S5. You'll need to figure out which revision you have. If it's rev. C and you can't find the schematic for it let me know and I'll email it to you.

Larry

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Last edited by rocketeer on Jun Tue 15, 2010 12:42 am, edited 1 time in total.

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 Post subject:
PostPosted: Jun Mon 14, 2010 11:17 pm 
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It must be a rev C as it uses the 1U5. The Photofact also has the 1U5. Here's the thing, the Zenith schematic is the one that came with the radio and shows both tube variations. There is still the difference in connections for the 40mf and 20mf electrolytics between the two. One is probably a typo, but I'm not sure which. Which electrolytic the 20mf or 40mf should have the postive end connected to pin 3 of the 3V4 vacuum tube?

Thanks for the fast responses.


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PostPosted: Jun Tue 15, 2010 12:31 am 
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Badrestorer's step-by-step H500 restoration will tell you everything you need to know, including info on the FIVE chassis variations:


http://antiqueradios.com/forums/viewtopic.php?t=115812&highlight=

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 Post subject:
PostPosted: Jun Tue 15, 2010 4:12 pm 
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rocketeer wrote:
There are at least three variations of the chassis in the ZTO H500. The early chassis has a 2-prong headset plug on the back. The later one had an RCA phono type jack. The third used a 1U5 tube instead of a 1S5. You'll need to figure out which revision you have. If it's rev. C and you can't find the schematic for it let me know and I'll email it to you.

Larry


There was actually one more variation--that has a tube socket for a 50A1 filament current regulator tube. This was a precursor to the 600 series, and based on the military model. These are fairly rare, but I have two of them.

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 Post subject:
PostPosted: Jun Tue 15, 2010 7:07 pm 
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Here are the five chassis variations, courtesy of Badrestorer's thread:

Introduction, baseline: Uses a 1S5 tube for the Det/AVC/AF. Has a dual-pin earphone jack.

Revision A: Uses a 1U5 tube for the Det/AVC/AF. Tube socket is wired differently from the 1S5. Also has a dual-pin earphone jack.

Revision B: Uses the 1U5 and earphone jack has been changed to a single 1/4-inch jack.

Revision C: Uses the 1U5 and has a single earphone jack. Low voltage switch was added for line voltages less than 110vac.

Revision D: Uses the 1U5, has single earphone jack and low voltage switch. A socket was added for an optional 50A1 ballast tube.

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 Post subject:
PostPosted: Jun Tue 15, 2010 9:45 pm 
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Thanks for filling me in on the variations. From what you have all told me, my H500 is a Rev C. Now, where should the postive ends of the 20mf and 40mf filter capacitors attach? One should go to pin 3 of the 3V4 tube. The other should go in between two 950 ohm power resistors. The Resistor is the metal one rivetted to the case with a center tap. One of my schematics has it one way the other is reversed. So far I've been trusting the Zenith schematic. But the Sams Photofact has me doubting this.


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 Post subject:
PostPosted: Jun Wed 16, 2010 5:56 am 
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Just connect them as they were when you got the radio. Chances are that it came like that from the factory.There's a better than excellent chance that the factory hooked them up correctly. My money is on the Zenith schematic being correct. There's no telling when the Sam's was made. You've got a great idea when the Zenith schematic was made. If all the voltages are off and/or a pretty bad hum is present, you'll know that you used the wrong schematic.

If it helps, I just checked the H500 I have in my "To Do" pile. Luckily, it happens to be a "Revision C" as described in Ed's post. The 40mf is connected to the 3V4. It still has it's original Zenith multi-section capacitor.

In short, if they were connected as per the Zenith schematic, that's the one you should use. Also, the schematic in the link from "antiqueradiobuff" is correct for your radio. It has the high and low voltage switch and shows the connections for the 1U5 as well as the 1S5. It's a multi-variation schematic with the variations noted on the bottom right corner. Remember not connect the electrolytic ground to the chassis. This radio has a "floating" ground bus.


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 Post subject:
PostPosted: Jun Wed 16, 2010 9:23 pm 
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Thanks Kent,

I would have attached them back the way they were when a got the radio, but I had already removed them from the cap. They were labelled by me with tags saying 20, 40, 60 and 200mf based on the zenith schematic.
I will connect it following the Zenith schematic as this corresponds to what you see in your H500 rev C.

Thanks again for taking the time to check your radio for this connection.


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 Post subject:
PostPosted: Jun Sat 26, 2010 11:43 pm 
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rocketeer wrote:
There are at least three variations of the chassis in the ZTO H500. The early chassis has a 2-prong headset plug on the back. The later one had an RCA phono type jack. The third used a 1U5 tube instead of a 1S5. You'll need to figure out which revision you have. If it's rev. C and you can't find the schematic for it let me know and I'll email it to you.

Larry


Isn't there a revision that used the 1U5 and dual earplugs?

Mike thats what I have or am I mistaken?


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 Post subject:
PostPosted: Jun Sun 27, 2010 12:22 am 
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That would be Revision A. See chart a few post back.

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 Post subject:
PostPosted: Jun Sun 27, 2010 9:40 am 
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Ed Morris wrote:
That would be Revision A. See chart a few post back.


gotcha. thanks.

Mike


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 Post subject:
PostPosted: Jun Sun 27, 2010 8:29 pm 
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[thanks
mike


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 Post subject:
PostPosted: Jul Mon 12, 2010 4:48 pm 
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It seems as though Revision D is the most rare?
They seem to be pretty hard to find.

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