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 Post subject: Oscillator Coil Open
PostPosted: Apr Sat 28, 2012 12:26 am 
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Location: Lafayette, Oregon
This is the oscillator coil out of a Philco 89. Here's the schematic.
http://www.nostalgiaair.org/PagesByModel/876/M0013876.pdf
One end of this coil (pins identified) goes to the cathode of the 36 Det. Osc. tube and the other end goes to an RC circuit to ground. I imagine to bias the cathode but tying it into the oscillator coil has me a little baffled.
Image

This section of the coil should read about 5.25 ohms. Mine reads open. My question is (and I hope I'm right) is the small coil that is pointed out in the picture the coil that is open? I think it's some kind of "tickler" coil? I'm hoping because it sure would be an easy one to rewind because it's over the main coil. This form has another form inside of it and it looks a little troublesome to seperate them.

Thanks,
Johnny

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 Post subject: Re: Oscillator Coil Open
PostPosted: Apr Sat 28, 2012 12:52 am 
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That is easy to rewind. Try to note the direction the coil is wound in from the leads and measure the thickness across the coil , then wind on a new coil with a small gauge of wire, 34 or 36 gauge enamel coated. These coils frequently open up on early philco radios, some glue or contaminate in the glue attacks the wire over time, thus the green areas you see on the coil.
Take your time and it will be a learning experience for you. :D

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 Post subject: Re: Oscillator Coil Open
PostPosted: Apr Sat 28, 2012 2:03 am 
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LarryC wrote:
That is easy to rewind. Try to note the direction the coil is wound in from the leads and measure the thickness across the coil , then wind on a new coil with a small gauge of wire, 34 or 36 gauge enamel coated. These coils frequently open up on early philco radios, some glue or contaminate in the glue attacks the wire over time, thus the green areas you see on the coil.
Take your time and it will be a learning experience for you. :D


Thinking that it is 13 turns on the coil. I use the wax from an old capacitor to keep the new coil in place. Just hit the end of an old capacitor with your soldering iron and drip a little wax on your new coil in a few places to keep it in place.

John k9uwa

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 Post subject: Re: Oscillator Coil Open
PostPosted: Apr Sat 28, 2012 2:20 am 
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Location: Charlotte,NC
Another way is to take a pin, or needle and run it across the coil. Count the number of "clicks" you hear. Each "click" is a turn of wire, giving you a good idea of how many turns to wrap the wire.

I just remembered where I found that tip: http://www.philcorepairbench.com/tips/svctip36.htm


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 Post subject: Re: Oscillator Coil Open
PostPosted: Apr Sat 28, 2012 4:24 am 
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Better make sure the secondary winding is good also. I just did my oscillator and antenna coil on a 84 because of the green disease on them. Took some time but really wasn't all that hard to do.

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 Post subject: Re: Oscillator Coil Open
PostPosted: Apr Sat 28, 2012 6:05 pm 
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Thanks guys! I posted a reply last night. Wonder where the heck that went. I've got the coil off. I counted 25 turns on the coil not counting the small pieces that kept falling off. Tried to figure them in. The form is cleaned up and I wanted to rewind it today. That's what my reply was about last night. It's been a long time since I've had to rewind a coil. Had to do all the coils in a Grunow 1151 a couple years ago. Maybe five years? Some of you may remember. That's where I learned what a "BIS" coil was. "BI-SELECTOR" coil!

Anyway my question was what is a good medium for use between the existing coil windings and the new one I'm putting over that? Looks like some kind of thin plastic would work.

EDIT: I remembered I used 35mm film as an underlayment for the new winding. I put 26 turns of 34awg magnet wire tightly wrapped around the form but did not terminate the 2nd end. I left about 18" in case I needed a turn or two more. I read about 2 ohms. Schematic calls out 5.25 ohms. How can this be? The width of my turns is very close to the original. A tad bit wider and as you can see in this pic my turns are tightly wound.
Image

Johnny

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 Post subject: Re: Oscillator Coil Open
PostPosted: May Wed 02, 2012 2:49 pm 
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Johnny wrote:
Thanks guys! I posted a reply last night. Wonder where the heck that went. I've got the coil off. I counted 25 turns on the coil not counting the small pieces that kept falling off. Tried to figure them in. The form is cleaned up and I wanted to rewind it today. That's what my reply was about last night. It's been a long time since I've had to rewind a coil. Had to do all the coils in a Grunow 1151 a couple years ago. Maybe five years? Some of you may remember. That's where I learned what a "BIS" coil was. "BI-SELECTOR" coil!

Anyway my question was what is a good medium for use between the existing coil windings and the new one I'm putting over that? Looks like some kind of thin plastic would work.

EDIT: I remembered I used 35mm film as an underlayment for the new winding. I put 26 turns of 34awg magnet wire tightly wrapped around the form but did not terminate the 2nd end. I left about 18" in case I needed a turn or two more. I read about 2 ohms. Schematic calls out 5.25 ohms. How can this be? The width of my turns is very close to the original. A tad bit wider and as you can see in this pic my turns are tightly wound.
Image

Johnny




So, did 26 turns of #34 wire work?

Ed


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 Post subject: Re: Oscillator Coil Open
PostPosted: May Wed 02, 2012 3:03 pm 
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Johnny wrote:
I left about 18" in case I needed a turn or two more. I read about 2 ohms. Schematic calls out 5.25 ohms. How can this be? The width of my turns is very close to the original. A tad bit wider and as you can see in this pic my turns are tightly wound.

Johnny


This coil you rewound Johnny isn't a tuned coil. Its just the pickup coil. So the exact number of turns on this one isn't all that critical. What is important is that you wound it the same direction as the original one. The Ohms stated on the schematic has to be wrong. It says the main coil is around 5 ohms also.. and its many times the number of turns and wire is about the same size. Finish off your coil wiring and put it back in the radio.. bet it works just fine.

John k9uwa

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 Post subject: Re: Oscillator Coil Open
PostPosted: May Wed 02, 2012 3:43 pm 
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To answer Ed's question... I won't know if it works until I get the chassis rebuilt. I'm still re-stuffing bakelite blocks at this point. Someone took the 75 socket out and put in an octal with a 6Q7. That had to be put back into original configuration. I've got a good week left then I'll come screaming for help again.

I agree John! I've rewound coils before. There's at least 100 turns on the primary and secondary of this oscillator and each side does read what the schematic calls out. Around 5 ohms. How can a 26 turn coil read 5.25 ohms? Gotta be a typo. I used the extra 18" I left on it and continued to wrap until I ran out of wire. Probably and extra 5 or 6 turns past the 26. It reads about 1.7 ohms. Must have been a dirty lead that gave me that 2 ohms because I've never seen 2 ohms again. I know I've got more then enough wire there and I expect it to work fine as it is but if I have to I have turns that can be removed. I made very good notes of direction, start and end points etc. as I unwound it. It came off of what I call pin 2, crossed to the bottom of the coil and then went CCW back up to the top of the coil to what I call pin 1. Rewound it just the opposite. I believe it's gonna be fine too. Find out soon enough.

Thanks guys,

Johnny

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 Post subject: Re: Oscillator Coil Open
PostPosted: May Mon 21, 2012 1:57 pm 
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Johnny wrote:
To answer Ed's question... I won't know if it works until I get the chassis rebuilt. I'm still re-stuffing bakelite blocks at this point. Someone took the 75 socket out and put in an octal with a 6Q7. That had to be put back into original configuration. I've got a good week left then I'll come screaming for help again.

Thanks guys,

Johnny



Wellllllll ??? How many turns did you finally end up using and did it work as expected ?? I ask because I have one that I was able to repair and I expect I will have to rewind it at some point.

Ed


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 Post subject: Re: Oscillator Coil Open
PostPosted: May Mon 21, 2012 5:02 pm 
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That's a great looking new winding. Just for information, with a coil such as yours, if you want to duplicate a winding, a convenient trick is to unwind the old winding if possible, then get some wire approximately the same gage (thickness) as the old winding, and cut the new wire to the same length as the old one. Use the entire length and this will result in the same number of turns, which is the most important characteristic of a coil. This is especially true when you are working on the tickler, or feedback, winding where the precise number of turns is not so critical.

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 Post subject: Re: Oscillator Coil Open
PostPosted: May Mon 21, 2012 5:24 pm 
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I've been letting the radio play for several days now and it seems to be playing fine. I put a total of 31 turns on it in case I had to remove some. Plays good so I left it alone.

I really believe that anywhere from 25 to 30 turns would work just fine. I know for a fact that I removed 26 turns of wire. But the schematic and it's reading of 5.25 ohms on that section kept throwing me of until I figured out that there was no way to obtain 5.25 ohms with 26 turns without uning 0-awg or larger. :)

Johnny

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 Post subject: Re: Oscillator Coil Open
PostPosted: May Wed 23, 2012 2:18 pm 
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Johnny wrote:
I've been letting the radio play for several days now and it seems to be playing fine. I put a total of 31 turns on it in case I had to remove some. Plays good so I left it alone.

I really believe that anywhere from 25 to 30 turns would work just fine. I know for a fact that I removed 26 turns of wire. But the schematic and it's reading of 5.25 ohms on that section kept throwing me of until I figured out that there was no way to obtain 5.25 ohms with 26 turns without uning 0-awg or larger. :)

Johnny


Thank you. I have that in my notes for future reference.

Ed


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