Knob shaft doesn't turn tuning coil
Posts: 65
Threads: 15
Joined: Feb 2014
City: Clayton, NC
Finally brought the Philco 71 back after a stay at my buddy's place getting repaired. Once home, I hooked it up to my signal generator to get it fine tuned. Turned the knob to the bottom of the AM band to run the signal test, but I went a little too far past the end of the dial. Suddenly, I couldn't tune the radio anymore even though the knob still wound. I assumed the dial cord had come off it's pulley, but that wasn't the case. Seems the shaft that the knob sits on no longer turns the turning coil. I can move the coil manually and everything works fine, but the knob shaft only spins by itself.
Any ideas on what might have happened or how to fix this?
Posts: 395
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Joined: Jul 2013
City: Horsham, PA
Does this knob have a set screw on the side? Perhaps that has loosened and it just needs to be tightened.
GL
Jon
Posts: 65
Threads: 15
Joined: Feb 2014
City: Clayton, NC
No, it doesn't unfortunately.
It's working a bit better this morning. It will turn the coil, but still slips occasionally. Unless you reach the end of the scale, at which point the shaft just turns freely. Have to manually move the coil before the shaft does anything again.
Feels like the shaft needs to be tighened or lubed with something heavy to make it stiffer. Not sure how to do that, as I'm still learning all this.
Posts: 2,128
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Joined: Oct 2008
City: Merrick, Long Island, NY
Please clarify. Is knob loose on it's shaft, or is the dial string just not being gripped properly(slipping?)
Posts: 65
Threads: 15
Joined: Feb 2014
City: Clayton, NC
The shaft is loose on the coil. The string itself seems to be fine. Most of the time, the shaft just turns freely and does not catch to turn the coil.
Posts: 411
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Joined: Sep 2008
City: Ironton Ohio
If the cord is slipping on the shaft, sometimes spraying it clean with contact cleaner helps, if that doesnt work you can buy dial cord conditioner, I cant remember where I bought mine because I have had it so long. It looks like a tube of chapstick that you rub on the cord, it works really good on slipping dial string.
Posts: 2,128
Threads: 18
Joined: Oct 2008
City: Merrick, Long Island, NY
You can move the tension spring one position closer to the center if this available, and borrow a chunk of rosin from any fiddler and touch up the string segment that is slipping.
Posts: 65
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Joined: Feb 2014
City: Clayton, NC
My wife plays the violn, so we did the rosin trick. It worked for awhile, but obviously that wasn't a permanent solution. Some other issues have cropped up since I posted this, so i'm gonna take the radio back to my buddy's place for another look. Hopefully we can figure it out then.
Posts: 2,128
Threads: 18
Joined: Oct 2008
City: Merrick, Long Island, NY
Well, once the dial cord comes off, might rough up the shaft where it winds aroundwith a little fine sandpaper. A tiny bit of grease on any pulley bearings along the trail aso helps. Probably should replace the cord if you remove it. Take pictures, make drawings, so you know how to get it back. Many use braided nylon fishing tackle line but you can buy "real" dial cord too.
Posts: 13,776
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Joined: Sep 2005
City: Ferdinand
State, Province, Country: Indiana
First of all, it isn't a tuning coil - it is a tuning capacitor (also called tuning condenser).
The drive assembly mounts to the front of the tuning condenser. It is desirable that the drive shaft (the part where the tuning knob fits onto) be loose and easily turned by hand.
These illustrations, from a page on my website illustrating how to restring the dial cord on certain Philco models, should help.
[Image: http://www.philcoradio.com/tech/images/dialdiag.jpg]
Not only does this show how the string should be routed, it also shows many parts of the drive assembly.
The dial itself is riveted to the dial holder. This is held in place on the tuning condenser shaft with a set screw. Make sure that set screw has not become loose, or else your tuning condenser will slip and not tune properly.
Another view:
[Image: http://www.philcoradio.com/tech/images/sideview.jpg]
This does not show the dial holder, but does show the shaft which drives the mechanism.
--
Ron Ramirez
Ferdinand IN
Posts: 65
Threads: 15
Joined: Feb 2014
City: Clayton, NC
Thanks, Ron! I'll print that out before my buddy & I have another look at it.
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