replacing some wiring on a Zenith 8A02 i need help

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replacing some wiring on a Zenith 8A02 i need help

Post by lmar701 on Wed Dec 05, 2012 9:25 pm

i understand the guage of wire is important when rewiring a tube radio (guessing due to resistance?)
before I get into this project, i would appriciate any additional information that would keep me from ruining this project
.

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Re: replacing some wiring on a Zenith 8A02 i need help

Post by Ken g on Wed Dec 05, 2012 9:39 pm

No .. gauge of wire is not to important . Just use stuff that looks close . I do know many Zenith radios have crumbling wire . I just guess you have read other sites that say you ''have to'' replace all of it . Thats hoarse poo . You only need to replace what is in bad shape . Try not to disturb most of it .

Its very important you do some minimal things to get the radio up & working before you go replacing alot of parts & stuff . When you work with a working radio you stand a much better chance to have it work when you are done .
As you work through it you can plug it back in & make sure it still works after a couple steps . If it doesnt , you dont have far to check for the problem .

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Re: replacing some wiring on a Zenith 8A02 i need help

Post by N7ZAL on Wed Dec 05, 2012 9:48 pm

Wire size is important in the old tube radios because of the larger currents. As mentioned, you can probably just "eye ball" the size and be in the ball park. FYI
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Re: replacing some wiring on a Zenith 8A02 i need help

Post by lmar701 on Wed Dec 05, 2012 9:58 pm

thanx N7ZAL

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Re: replacing some wiring on a Zenith 8A02 i need help

Post by lmar701 on Wed Dec 05, 2012 10:03 pm

Ken,
ALL of the wire insulation has crumbled. gonna de-solder one end of each wire then slip some shrink tubing over them. a few wires are broken and/or missing. i will do that before I spend any other cash. thanks for the input...

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Re: replacing some wiring on a Zenith 8A02 i need help

Post by N7ZAL on Wed Dec 05, 2012 10:41 pm

Sounds like a good approach!
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Re: replacing some wiring on a Zenith 8A02 i need help

Post by stringbender31 on Wed Dec 05, 2012 10:53 pm

Anywhere from 18 to 22awg usually works for me, just be sure the wire is rated for the proper voltage.
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Re: replacing some wiring on a Zenith 8A02 i need help

Post by Resistance is Futile on Wed Dec 05, 2012 11:22 pm

Since most wire runs are very short, the current carrying size isn't to important per-say. A short wire can handle a lot of current compared to say 7 foot of wire. Since most radios only handle 50-150 Ma for the heaters and a few Ma for DC there is not much to be concerned about, HOWEVER the voltage insulation of wire is of concern. Don't use anything less than 250 volts insulation. Even the power cords can be 18 gauge.
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Re: replacing some wiring on a Zenith 8A02 i need help

Post by repairtech on Thu Dec 06, 2012 11:33 am

Sets with parallel filament wiring should be re-wired with an appropriate gauge wire - dressed down against the chassis and if floating, should be twisted pairs to reduce hum issues.

Single-line filament wiring should also be dressed down against the chassis for the same reason.



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Re: replacing some wiring on a Zenith 8A02 i need help

Post by Guest on Thu Dec 06, 2012 12:49 pm

should be twisted pairs to reduce hum issues.

I'm glad you mentioned this, most people I run into do not know how important it is!

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Re: replacing some wiring on a Zenith 8A02 i need help

Post by Resistance is Futile on Thu Dec 06, 2012 2:48 pm

especially around the audio.
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Re: replacing some wiring on a Zenith 8A02 i need help

Post by lmar701 on Fri Dec 07, 2012 8:45 pm

I have to tell you this is my first project. I have no idea what parallel filament wiring, Single-line filament wiring, dressed down against the chassis and floating, means. and what pairs should I twist? Please excuse my ignorance.


Last edited by lmar701 on Fri Dec 07, 2012 8:47 pm; edited 1 time in total (Reason for editing : mistyped)

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Re: replacing some wiring on a Zenith 8A02 i need help

Post by Ken g on Fri Dec 07, 2012 9:00 pm

Its interesting where i find several radios without the filament wires twisted and those radios dont hum . Lets not confuse this guy . Just use wire that looks like the old if you need to replace any .

How did ''every'' wire in your radio crumble ? I have worked on hundreds of these Zeniths and others with stiff wire and never found one with every wire crumbled off . Someone must have been having fun with that one .

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Re: replacing some wiring on a Zenith 8A02 i need help

Post by N7ZAL on Fri Dec 07, 2012 9:07 pm

Just use wire that looks like the old if you need to replace any .

I agree. Don't worry too much about the terminology, that will come with time. A twisted pair is just 2 wires that are twisted together. Think about putting 2 wires in a drill and then turning the drill on. The wires will twist. Twisted wires tend to cancel out noise.
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Re: replacing some wiring on a Zenith 8A02 i need help

Post by Guest on Fri Dec 07, 2012 10:41 pm

The schematic/service info will usually specify if there are any critical wiring, dressing, or routing issues with a particular set.

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Re: replacing some wiring on a Zenith 8A02 i need help

Post by Bill Cahill on Sat Dec 08, 2012 2:00 am

Alright. It's time to make some clarification........
First, always dress the wiring, as a whole, the way the original wiring was dressed. If the wires were twiwted together, do it the same way.
Neatly dressed wiring against the chassis should stay that way.
If it is in mid air, you need to do that, as close to original length as possible, and, shaped the same way. This includes critical circuits such as the oscillator, and, RF tuning circuits.
Not very many of these radios were originally overly neat on wiring. It would have added to costs. Yes, there are definitely critical wires, which by the way, very few schematics tell about, but, use some common sense.
Try to use the same style, size wiring as originally used. In some circuits, it's also good, but, not crittical to use the same color wires as original. The colors won't stop the radio from playing, but, makes it easier for tracing purposes.

Now, about the filaments. AS a rule, but, not always, if there is no power transformer, the filaments of the tubes are in series. That is if you were to un plug any tube, the rest of the filaments will also go out.
If your set has a power transformer, usually, but, again, not always, if you pulled any of the tubes out, the others would remain lit. That is because all the filaments are wired in parallel. That is, across one another.In comparison, a series string set will have all the tube filaments wired as a single wire going from one of the filament pins of the preceding tube, to a filament pin of the next tube. Then, the other filament pin of that tube will go to one filament pin of the next tube, etc.. It's like series Christmas lights. If one bulb burns out, the whole set goes out.

There were, however , a very few sets where they used a power transformer with the tube filaments wired in series. I once had such a set sold by Silvertone in the 40''s.
That set had several more tubes, and, to make it easier on manufacturer, they used a higher voltage power transformer , and, put the filaments in series. The good news is radios like that are rare.

Neatness is important. But, as a rule, I would never recommend wiring it any differently than ilt was originally wired. There are some exceptions, of course. I hope this helps.

And, for the books, as a rule, the only way wires can lose all their insulation is if they are moved. However, I have had some radios, which includes Crosley's, a cheap table model RCA Victor, and, some GE radios where a lot of the rubber fell off just from heat, and, age.
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Re: replacing some wiring on a Zenith 8A02 i need help

Post by Guest on Sat Dec 08, 2012 8:25 am

Bill, that was a great post! Did you ever think of going into teaching? Smile

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Re: replacing some wiring on a Zenith 8A02 i need help

Post by Bill Cahill on Sat Dec 08, 2012 10:57 am

Nah. I know little thory, and, I failed math. I work on knowledge gained over the years from others, and, what I've learned on my own.
I know alot, and, I guess you could call me at least a semi professional, but, there's still alot I don't know.
I'm lucky I've learned all I have, and, I've had enough experience that I can tell where to look for problems. I'm good with the meter, and,am working on scope learning.
I know test equipment such as signal generators, and, such.

I have learned a lot, and, love sharing my experience with others.

By the way.... In my list of some of the nastiest radios, I forgot one outstandly nasty one I own.
It's a Philco AC DC table model set. In other words, series string.
It's a two band radio with push butytons on top, and, a wood case.
This radio was un molested, and, every single rubber wire in that set has dis intergrated! And, they have a special am loop antenna with alot of rubber wireds going in, and, out that are stark gravely bare!
I looked at the bottom of the chassis, and, it wasn't pretty.
The radio is static display in my house. I just don't have the patience for it.
Yet, I'll work on nightmares like my Admral, and, my 6T74 RCA Victor "family" tv.
Bill Cahill

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Re: replacing some wiring on a Zenith 8A02 i need help

Post by Resistance is Futile on Sat Dec 08, 2012 3:28 pm

lmar701 wrote: I have to tell you this is my first project. I have no idea what parallel filament wiring, Single-line filament wiring, dressed down against the chassis and floating, means. and what pairs should I twist? Please excuse my ignorance.

This is to re-enforce the main (excellent) points that Bill described.

Parallel filament wiring= If the radio has a power transformer then usually it has a low voltage output that is either 6 volts or 12 volts. Each tube has two connections for the filament. These are usually run with the filament connections in parallel. If one tube filament burns out the rest still keep working.

Single Line filament wiring= Radios without a power transformer take the 115 volt line and put the tubes filaments in series. Each tubes connection goes from one filament connection to the next, just like the old Christmas tree lights used to be. If One tube burns out then non of the other tubes will light, because the voltage is interrupted because one filament can no longer conduct electricity. Usually You will find the the tubes have different filament voltages.
The normal tube numbers all add up to 115 volts (50C5---12V6---12AV7---35L5---12sk7).
So mathematically --> 50+12+12+35+12=115

Dresses down against the chassis= Dressed means to lay the wire neatly next to the chassis.

Floating= means the wires can just be connected from point to point up off the chassis. (sometimes grounding wires are done this way to avoid using the chassis as common ground)

Usually AC wires for the filaments are Twisted pairs (wrapped around each other), the reason is as one wire has the positive going pulse the other has a negative going pulse, induction from one wire next to the other has a canceling effect for induced hum.

Hope this helps you. santa
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Re: replacing some wiring on a Zenith 8A02 i need help

Post by lmar701 on Thu Dec 20, 2012 5:12 pm

thanks for the terminology schoolin', quite helpful.

i cant figure out how to post pictures. any suggestions

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Re: replacing some wiring on a Zenith 8A02 i need help

Post by lmar701 on Thu Dec 20, 2012 5:25 pm

upon closer inspection, I should be able to slip shrink tubing over most of the wires in need of repair. However some of the wires will have to be replaced. In either case, the color is virtually indistinguishable amoung the existing wires. I have found several schematics but they only depict voltages, resistance, pin numbers etc...
is there somewhere to find the colors?

secondly, the only wire i can find locally is 600V, with thick insulation, and pretty stiff. where do i find wire more like the original?

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Re: replacing some wiring on a Zenith 8A02 i need help

Post by Bill Cahill on Thu Dec 20, 2012 6:33 pm

Try antique electronics, or, radio shack. There are several on line places that sell similar wires in plastic insulation.
Generally, as a rule, AC wires are either brown, or, tan.
B- tends to be black.
B+ is red.
Wires going to plates are Blue.
To control grids, low voltage, that is, green.
Now, this isn't always, but, that's as a general rule.
That wire is too heavy for an ac dc set.

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Re: replacing some wiring on a Zenith 8A02 i need help

Post by GaryRabbitt on Wed Jan 23, 2013 10:37 pm

lmar701 wrote:thanks for the terminology schoolin', quite helpful.

i cant figure out how to post pictures. any suggestions
Post your photos on any internet accessable location. Photobucket, Picasa, whatever, there are thousands of sites that will store your photos for free.

Upload the photo. Try and have it 600x800 max size so it is not oversized on the forum page.
Bring up yout image, rt click on it, go to properties, to get the URL address of the photo itself. (NOT the page address). Copy the URL of the photo, come to your post and paste it in the text box.
Add 2 "image tags" on each side of the address.. [img ] your address goes here, no spaces between the tag and address [/img ] (I had to add spaces so you can see how the tags look)
Your photo will appear in the post.

Photobucket and others might have a line you can copy of the location of the hoto. Use that feature, then paste in your text box. The tags are usually added automatically.
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Re: replacing some wiring on a Zenith 8A02 i need help

Post by Bill Cahill on Wed Jan 23, 2013 11:14 pm

Photobucket has a link. When you point to the picture you want to copy a box pops up. Go to bottom link that says image, or img.
Left click on that. Goe to your post in the forum that you are writing, and, right click on that. Select Paste. Left click on past. It pastes in the correct img link.
Each time you add pictures, skip two spaces below, and, repeat same process with the next picture, or, pictures, one at a time.
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Re: replacing some wiring on a Zenith 8A02 i need help

Post by GaryRabbitt on Wed Jan 23, 2013 11:23 pm

Yes, just make sure your image is 800 wide max, or else we will have to scroll way off to the right to se the whole photo. Some don't even bother to look if the size is not right.
On the ARF, sometimes a new member will post a shot of a radio. All we will see is half of a knob, and have to scroll. That happens when your image is 3000x4000 Smile
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