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 Post subject: Zenith 12H090
PostPosted: Jan Mon 18, 2010 1:58 pm 
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Location: Willington, CT USA
Hi all-
I just picked this console up over the weekend, and I'm going to start going through it.
It has the lovely crispy rubber covered wire, so it's going to have to be totally re-wired.
Anyway, this set has the 11C21Z chassis so no field coil on the speaker.

My question is, what is the small box mounted on springs with one tube and a can cap sticking out of it for? I don't see this on the schematic (Rider's). It has a harness with a plug on it, but it's not shown on the schematic. Is there a newer schematic since I assume this is a later model chassis?
Any info would be appreciated.

BTW: I assume 300v wire is fine for re-wiring this set, #18ga.??

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PostPosted: Jan Mon 18, 2010 2:10 pm 
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Where does it plug into.? And the wire will be fine, David

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 Post subject:
PostPosted: Jan Mon 18, 2010 2:19 pm 
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Location: St. Louis, MO, USA
The sub-chassis on springs with tube is the oscillator for Zenith's Cobra "Radionic" phono pickup system. It's quite different from any other phono pickup. Info is usually included in the service material for the turntable, model number of which will be S-something and found in Rider's.

Example: model S-11680
http://www.nostalgiaair.org/PagesByMode ... 025631.pdf

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 Post subject:
PostPosted: Jan Mon 18, 2010 4:36 pm 
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Thanks Guys!
Well, since I don't have the turntable for this unit I don't think I'll be needing that part (at least for now).
Can I run the radio without the oscillator unit plugged into the harness?
Unfortunately the cabinet is shot on this unit, so I'll probably make a slimmer cabinet to hold just the radio, speaker, and Wavemagnet.

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 Post subject:
PostPosted: Jan Mon 18, 2010 4:57 pm 
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Location: Willington, CT USA
Since I need to re-stock wire anyway, I see Radiodaze has a nice assortment of #22 ga. 600V wire for $29.50.
It looks like the current carrying capacity of #22 ga. is anywhere from 5-7 Amps depending where you look. Looks like plenty enough for radio chassis work.
This is going to take some time :)

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 Post subject:
PostPosted: Jan Thu 21, 2010 1:32 pm 
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Location: Willington, CT USA
Does someone happen to have a clearer scan of the Riders schematic for this set? It's on pages 15-91,92.
I can't read a lot of the cap values/voltages on the list on the left side of the schematic from the Nostalgia Air copy.

Also, I have chassis 11C21Z if this makes any difference.

Thanks in advance.

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 Post subject:
PostPosted: Jan Fri 22, 2010 1:11 pm 
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Location: Willington, CT USA
I have a question on a few capacitors in this chassis.
The cap is C39, and it goes on the primary side of the OT from the CT to one side of the winding. Now the schematic calls for 1000v rating, is a ceramic 1Kv disc cap okay for use in this position?

I also question the .0001uf cap (C24) that goes from one leg of the line to the FM antenna, should this be replaced with a safety cap? I would think so just by looking at it's use. I know that the line to chassis cap (C38) should be a safety cap.

Last one is the power supply filter caps, is 47uf too large of a change from the original 40uf? I looked at the GE data sheet for the 5Y3GT rectifier, and it gives a value for the first filter cap as 20uf.

Sorry for all the questions, I'm still learning some of the finer points of this hobby :)

Schematic is here:
[url]http://www.nostalgiaair.org/Resources/view.asp?FN=\M0024713.pdf[/url]

Not sure why the URL above won't link.

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 Post subject:
PostPosted: Jan Fri 22, 2010 3:25 pm 
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Location: Detroit, MI USA
Yes, you can use a 1KV disc ceramic to replace the cap at the output transformer.

It would not hurt anything to use a safety cap for the one coupling the antenna to the power line.

There's usually no problem in replacing 40uf with 47 uf, the tolerance on the originals is sometimes as great as +50% or even +100%.

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Dennis

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 Post subject:
PostPosted: Jan Fri 22, 2010 4:19 pm 
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Thanks Mr. D
I just like to confirm my thought process with more "seasoned" professionals :)

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 Post subject:
PostPosted: Mar Mon 01, 2010 1:41 pm 
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Location: Willington, CT USA
I'm almost finished with this set, and everything works very well.
I like the interesting tuning eye tube with the four square tuning quadrants.

The tuning mechanism uses a rubber wheel that presses against the metal shaft that the tuning knob is on. The rubber kind of works, but slips a little. Anyone have any tips on how to make the rubber a little more tacky? It reminds me of the pinch rollers on RTR decks, they get a little glazed with age. I tried 100% alcohol to clean it and it helped it a little but but I need a little more "grip".

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 Post subject:
PostPosted: Mar Mon 01, 2010 2:53 pm 
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I use stronger solvents than alcohol, which is basically useless on hardened rubber. Many times something chlorinated works well, might try a bit of brake cleaner on a rag. Also you can make the surface more aggressive by roughing it up slightly with sandpaper to remove the glaze.

I have ended up needing to replace that rubber drive on many of these when all efforts to clean failed. Fortunately I was able to find better ones from junked out sets.

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Dennis

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 Post subject:
PostPosted: Mar Mon 01, 2010 3:53 pm 
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Location: Willington, CT USA
I tried sanding, but I guess it could use some more. This is probably what got it working better than before.
I like the brake cleaner idea. I've heard on RTR forums that alcohol will remove the plasticizers in the rubber making it harder than before. Never had any problems using it though on the pinch rollers of my RTR's though.

Thanks for the reply.

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 Post subject:
PostPosted: Mar Mon 01, 2010 5:22 pm 
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Location: Detroit, MI USA
In the shop we always used carbon tetrachloride, used to buy it in gallon cans. That was the best available cleaner for rubber phono drives and belts, even worked well as a control cleaner. There was another solvent sold by G-C called Chloro-Kleen which appeared to be just about the same thing, and worked nearly as well.

Of course carbon tetrachloride also turned your skin white, which is not a good thing, and it is no longer easy to get because of toxicity problems.

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 Post subject:
PostPosted: Mar Mon 01, 2010 6:34 pm 
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Location: Willington, CT USA
Ah yes, good old Carbon Tet.
We used to have a heated bath of that to degrease engine blocks in before re-machining and rebuild. It's a good solvent!

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 Post subject:
PostPosted: Mar Mon 01, 2010 9:35 pm 
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Joined: Jan Tue 16, 2007 11:48 pm
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Location: Hueytown, AL
Carbon tet. Radio man's universal cleaner BQ. (Before Quietrol) Red liquid in an about 3 oz. bottle with an eye dropper cap.


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 Post subject:
PostPosted: Mar Tue 02, 2010 2:46 am 
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Posts: 7941
Location: Dayton Ohio
Hi Glennn, You can try a rubber revitalizer product such as the one about halfway down this page.

http://www.action-electronics.com/lubricants.htm

I remember using such a product and soaking idler tires and belts in the stuff to bring the grip back to the rubber.
It might help that wheel.

-steve
ka8riz


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 Post subject:
PostPosted: Mar Tue 02, 2010 1:15 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Willington, CT USA
Thanks Steve!
I just ordered some. I'll also give this a try on my RTR tape deck pinch rollers.

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