ohohyodafarted
12-23-2008, 06:12 PM
As any CT100 collector will tell you the design of the fine tuning knob on these sets by RCA was a real disaster. The fine tuning knob on these sets slips over a bakelite rotary cam that has a keyway on it. This cam drives the fine tuning coil through a series of levers.
The cam has only one keyway, but for some reason RCA decided to place 3 slots in the throat of the fine tuning knob and as a result, the throat of the knob is very prone to breakage. Had the knob been designed with only one slot, the throat would have been much stornger.
As it is, if you apply too much torque to the knob the prongs between the slots will break off.
I have 3 of these and all of them were broken to one degree or another. After thinking about the issue for a while I came up with a very elegant soultion that not only fixes the knob, it makes it better than the original.
The basic material is a hunk of 1.5" OD by 1/4" wall 6061 aluminum tubing. Placed on the machine lathe I bore out the ID's with a boreing bar so that it fits the OD of the knob throat and the OD of the bakelite cam on the tuner.
AFter turning the part to the correct ID's it is cut to length and then it is placed on the milling machine. Then a slot is milled in the end that faces the tuner, which mates with the keyway on the bakelite fine tuning cam.
Any remaining fingers on the throat of the knob are ground off as shown in the photo of the knobs. Then the new aluminum knob throat is slipped over the shortened plastic throat of the knob and cemented in place with 5 minute epoxy.
The result is a knob that is strong and works better than the original.
The cam has only one keyway, but for some reason RCA decided to place 3 slots in the throat of the fine tuning knob and as a result, the throat of the knob is very prone to breakage. Had the knob been designed with only one slot, the throat would have been much stornger.
As it is, if you apply too much torque to the knob the prongs between the slots will break off.
I have 3 of these and all of them were broken to one degree or another. After thinking about the issue for a while I came up with a very elegant soultion that not only fixes the knob, it makes it better than the original.
The basic material is a hunk of 1.5" OD by 1/4" wall 6061 aluminum tubing. Placed on the machine lathe I bore out the ID's with a boreing bar so that it fits the OD of the knob throat and the OD of the bakelite cam on the tuner.
AFter turning the part to the correct ID's it is cut to length and then it is placed on the milling machine. Then a slot is milled in the end that faces the tuner, which mates with the keyway on the bakelite fine tuning cam.
Any remaining fingers on the throat of the knob are ground off as shown in the photo of the knobs. Then the new aluminum knob throat is slipped over the shortened plastic throat of the knob and cemented in place with 5 minute epoxy.
The result is a knob that is strong and works better than the original.