Topic: Fixing the tuning dial on the radio

[sparky65]

So I started to dig into my AM radio in order to start repairing it.  Turns out electronics wise it works great.  Some cut wires but they are an easy fix.  The issue I have is the radio tuning knob contraption. 
From what I can tell the large plastic gear at one time had a tab that keyed it to the metal disk.  When you turned the knob the plastic gear would turn the metal disk which was pressing against the rubber washer which in turn was moving the outer metal disk which is part of the actual tuning shaft.  As I understand it the purpose of this friction setup was so that when the preset buttons were pressed the plastic gear would be pulled away from the metal disk so that the tuning shaft wouldn't try to back drive the knobs.  My problem is it is broken and there seems to be no way of replacing just this plastic piece without replacing the whole assembly.  Since the rest of the radio works I am thinking of trying the following.  I want to drill two holes through the entire assembly ( metal disk, rubber disk and plastic gear) approximately 180 degrees apart.  Then put two screws through the whole assembly with a lock nut.  I'd leave the lock not loose so that the gear would still slide on the screws.  In order to drill these holes and install the screw I may have to drill through the side of the case.  It depends on how much slack I can get on the wires.  Am I crazy for trying this?  Is the plastic just going to break on me?  Anyone else have a better idea for a fix?  If I do have to drill holes in the case I dont believe it would be noticeable once installed.

[69RavenConv]

I just took a look at my 1969 Philco AM radio which appears very similar to your 67 (?).  Mine has a metal arm with a 90 degree hook on the end that fits in the groove on the plastic gear -- just to the right of the embossed "C" in your picture. It appears to be missing in your unit. When a tuning button is pressed, it's this arm that pulls the gear away from the discs and allows the clutch to slip. If I follow you correctly, I would think running a pair of  rigid fasteners through all the plates would defeat the purpose of the clutch, forcing  the gear to turn with the presets, no?

[sparky65]

The arm is there.  Its directly under the gear so a little hard to see.

When a tuning button is pressed, it's this arm that pulls the gear away from the discs and allows the clutch to slip. If I follow you correctly, I would think running a pair of  rigid fasteners through all the plates would defeat the purpose of the clutch, forcing  the gear to turn with the presets, no?

You see that's my question.  Why the clutch.  I dont see a problem with the plastic gear turning because when the arm pulls the gear it also disengages it from the teeth on the tuning knob.  So I dont see why it would matter if the plastic gear turns as long as it doesn't engage the knob.  Maybe something else isn't right on this unit.

[jwc66k]

I like your style, but I would be more inclined to find another radio and use it as is if it worked, or use it for parts.
Jim

[69RavenConv]

The arm is there.  Its directly under the gear so a little hard to see.

You see that's my question.  Why the clutch.  I dont see a problem with the plastic gear turning because when the arm pulls the gear it also disengages it from the teeth on the tuning knob.  So I dont see why it would matter if the plastic gear turns as long as it doesn't engage the knob.  Maybe something else isn't right on this unit.

I think I see what you're saying now. The preset mechanism works but twisting the knob doesn't. The gear, inboard disc and rubber disc should turn as an assembly (turning the outboard disc thru the clutch) but they don't. Removing the guts and tearing down the clutch would probably reveal a solution but Jim's advice is probably the best. Salvaged AM radios are  pretty easy to come by.