Problem du Jour: Stiff Tuner
 

After the radio was completely assembled the tuning knob was slipping a bit in some spots. I snugged up the dial cord, but gang condenser kept getting harder to turn. Tried various lubricants including cleaning and regreasing the ball bearing joint. It just get worser and worser.
There are three bearing points, and I can't be sure which is the problem, but I suspect it's the ball bearings. The plates for sure don't bind.

https://lh6.googleusercontent.com/-2...-10%252040.jpg

It's clear that I don't know what I'm doing here, so does anyone have any suggestions before I screw it up further? I've got 3-in-One, SAE 20 and 30 oil, automotive lithium grease, white lithium grease and all-purpose spray lube.

Thanks,
Winky, the Eternal Novice.

The front ball bearings and single rear ball should be flushed out with solvent and then relubed with white lithium. The solvent can be CRC Electronic Cleaner (auto parts store) or even WD-40. Stuff paper towels in the area to soak up the drips first. The center contact just needs a couple of drops of contact cleaner: this is where the frame has to make good electrical contact with the rotor.

If the action is still stiff (you're sure it's the condenser and not the string and other pulleys? Test condenser by itself with no string.) look to see if there's a nut with center adjustment screw on the rear behind the single ball. If so loosen the nut just a little and then loosen the center screw just a tad and hold it there while retightening the nut. You have to watch that you don't disturb the plate spacing when doing this.

I took the unit off the chassis to eliminate extrinsic causation. There is no adjustment for pressure on the bearings. I have a big can of CRC cleaner, so I'll give it thorough flush. My 40-year-old white grease is actually yellow-brown-tan, so I might spring for some new grease.

Thanks,
Winky

Ultrahyposonic Wedginator
 

Thorough flush of bearings made little difference so I had to go high tech with the ultrahyposonic wedginator.


With a few judicious taps on the wedginator, the condenser rotates freely. To attempt permanent distortion of the cast metal frame I tapped the wedge in a little further and one of the ball bearings came out and tried to escape by rolling across the floor. Fortunately I have a handy magnetic ball bearing retriever, and I managed to find the ball bearing and get it back in place.

https://lh5.googleusercontent.com/-1...-10%252042.JPG

With the wedge removed there's some improvement. I'll let the wedginator stay in over night and see if I can get some permanent distortion.

Thanks again.

-Winky

On second thought...
 

On second thought, looking at the thickness of the cast metal, I realized that I wasn't going to bend it without breaking it. I was trying to figure out how to make a metal brace to push the side of the frame a few microns apart, but I thought that might offend the gods of capacitance.

Then I had an "Aha!" moment. Cut up one of those plastic trimmer adjuster things and wedged two pieces in where they don't interfere with the tuner mechanics. They seem stable, but I added some JB Weld to help keep them from wiggling loose. The thing turns freely with this little bit of pressure on the frame.

https://lh6.googleusercontent.com/-p...-10%252044.jpg

If I can find all the pieces to put the thing back together tomorrow, then I'm done.

- Winky

Ole! That was going to be my next threat, to gently jack the ends apart. Wonder how that got jammed together so much. I don't think that's cast: it's thick and just bent on a brake. Looking at the edges of the frame you can see it was sheared.

This is mechanical geniousity at work. How did you figure out that the frame was smooshed together in the first place? What if it was instead widening and needed to be smooshed to restore order? Was it just trial and error or is there some secret here?

Credit goes to Reece. He mentioned an adjustment screw. There's no screw, so I tried an alternate way to adjust it. Maybe the dimensions hadn't changed, but the end bearing was damaged from 75 years of grit and grime.

I can't envision needing to narrow the frame, but I'd probably take off the rotor and whang the frame with a hammer.

Incidentally, after I put it back together, two or three rotor plates were touching stator plates. I had to go back and lighten the separating pressure by shortening (shaving the end) of one of the plastic posts. And I still had to manipulate the plates to get them adequately separated.

I've suspected that the stator part of the cap is soldered in place during manufacturing, and that they may have used thin plastic or paper inserts to position the stator caps plates just before soldering. Look at the solder globs between the metal pieces crimped to the reddish brown insulation and the metal frame of the stator cap, just above where you put your plastic spacers.
https://lh6.googleusercontent.com/-p...-10%252044.jpg

Solder Globs?
 

Not sure what you're verbally pointing at. Here's a little higher resolution of the same area.

https://lh3.googleusercontent.com/-U...-10%252045.jpg

I am sure that they made this radio as cheaply as they could.
- Winky

http://www.videokarma.org/attachment...1&d=1358831468

The areas I'm pointing to with the Yellow arrows.

There were plenty of tuning caps made that way with no axial adjustment but I can't remember running into one that was out of whack. Guess you win the prize, Winky! The "a little bit better" ones have the adjusting screw and lock nut on the back.