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Radio Dial Mechanism
November 1953 Radio-Electronics

November 1953 Radio-Electronics

November 1953 Radio-Electronics Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Electronics, published 1930-1988. All copyrights hereby acknowledged.

Unless you are into restoring and/or repairing radios with dial cords, you probably can't fully appreciate the humor in this short piece from a 1953 issue of Radio-Electronics magazine. Dial cord is a type of string that does not stretch when put under tension. It is wound around the shafts of two or more components to keep them in step with each other. Since the advent of LED and LCD readouts for displaying the tuned frequency, there was no need to mechanically synchronize a sliding or rotating pointer with the position of a (usually) multi-plate tuning capacitor. If you are/were lucky, the path of the dial cord simply wrapped around the shaft of the tuning element (capacitor) and around the axle of a circular tuning dial, with no pulleys or bobbins for changing the direction. Such is the case with my Crosley 03CB console radio. Nightmare scenarios, as jokingly referred to in this story, are like that of the dial cord in my Realistic Patrolman−50 AM/FM/Shortwave radio where the path was a torturous set of windings clockwise two times around one wheel then around the direction-changing pulley and three winds in a counter-clockwise direction on the next wheel, etc., etc., etc. That was while keeping the cord at just the right tension to assure smooth operation without any slipping or binding.

Radio Dial Mechanism

Radio Dial Mechanism, November 1953 Radio-Electronics - RF CafeNational Service Manager

Superoptic Radio and TV Corp.

Ninety Six, S. C.

Dear Sirs:

Thank you very kindly for the instruction sheet which you enclosed with the new dial cord and pointer kit for replacement in your model T-175. There is some question, however, as to the completeness of the installation procedure as outlined on the sheet. The following are a few points that might be added:

First, as the cord is grasped firmly in the left hand and the dial spring is held in the right hand (as shown in the instructions), I found no trouble in threading the cord around drum A, through eyelet 3A and under slider X. However, I think it should be noted that in order to cut the cord at W while spring R-1 is stretched to 1.1 inches and the dial pointer is located at 720, it is necessary to transfer the cord (W-1) so that it is held between the teeth, so the left hand is free to cut the cord at H.

Also, since the dial drum tends to move while stretching spring R-1, it is necessary to remove one shoe (preferably the right) and place the big toe through cutout S-1, under plate 7 of variable capacitor C17A, being careful not to bend the plates with the toenail. A note of caution is also necessary in the instructions for stretching tension spring B-7 to point A; since in case the spring is pulled beyond point A, serious injury may result to the right elbow (required to hold drum C from falling off shaft T while set-screw S-19 is loose). In addition it should be advised that a first-aid kit be kept handy while looping cord 2 through hole F and around drum G. It seems that this procedure often causes heavy pressure on springs L-1 through L-7, resulting in their flying in all directions around the room.

My second suggestion is to provide a procedure for setting the dial pointer P1 to indicate 720 on the dial. Since it is required to set the pointer before cutting the dial cord, and since the cord cannot be cut until spring R-1 is stretched to exactly 1.1 inches, some difficulty may be encountered. Remember that the left hand is holding cutting pliers; the right hand is stretching spring R-1; the teeth are holding cord Y; the left knee is preventing the chassis from falling off the table; the right elbow is holding drum C on shift T; and the right toe is inserted in cutout S-1 under plate 7 of variable capacitor C17A. It is therefore necessary that a board (not supplied with kit) be propped up behind the dial plate between J and D to apply pressure to the slider at Z. This will hold the dial pointer exactly at 720. Extreme care must be taken in placing the board on the slider since the board will tear the speaker cone completely off the speaker frame if it slips.

After cutting the dial cord (at point was shown on the instructions) it was found that a note of final warning should be included on the instruction sheet. The heavy tension caused by spring R-1, when stretched to 1.1 inches, results in the sudden revolving of dial drum C (despite the pressure of the elbow against it). Dial drum C will then spin off of shaft T and spin across the front of the chassis, breaking tubes V1, V2, and V3, unless they have been removed.

Also, please note my order for another installation kit of the same type - the original was ruined when the cutter slipped. Please send the kit as soon as possible, since my physician advises me that I will be on my feet again in a few weeks.

Very truly yours,

Herbert Michels

 

 

Posted October 12, 2020

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