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Mr2001
12-02-1999, 07:20 PM
I recently came to own a car radio from the early 80's, and I can't figure out how the mechanical preset buttons work.. you know, the kind where you pull it out and push it back in to change the setting. What's the secret?

Searching the vast knowledge of the Internet hasn't worked so far, because every time I do a web search that includes "radio" and "buttons", I get results about the computer GUI buttons. *sigh*

pmh
12-02-1999, 09:48 PM
It's kind of hard to explain. You really need to see it, but here goes:

The tuning knob is connected to a rotary variable capacitor that changes the radio frequency with a loop of string (think of a fanbelt). The station pointer is anchored to the string and one point of the loop is anchored to the preset buttons' mechanical linkage mechanism.
This mechanism is the real magic. I won't even try to explain it. If you're really curious, get an old $5 AM radio from a junkyard and take it apart. It's fascinating and inspires respect for "primitive" (pre IC) technology.
Anyway the mechanism operates in such a way that when a button is pulled out it disconnects from the string link and when pushed in it reconnects to the the link. (In effect, it "lets go" of the string at the "old" position and "grabs" the string at the "new" position.) Then, whenever the button is pushed again the mechanical linkage returns the string to the position it was in when that button was set (and thus moves the capacitor to re-tune the radio).

Hope that helps (or at least doesn't confuse you further.)

John W. Kennedy
12-03-1999, 11:57 AM
Some non-car radios had presets that worked a different way. They were electric switches (with a mechanism to disengage each other) connected to preset capacitors that you tuned with a screwdriver in the back.

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John W. Kennedy
"Compact is becoming contract; man only earns and pays."
-- Charles Williams

Ukulele Ike
12-03-1999, 12:01 PM
Interesting. When I read the OP, I figured Mr2001 just wanted to know how to set his radio, not the theory behind its operation.

If that's the case....tune the radio to a station you want, using the knob on the right. Pull the first button out, then push it all the way back in. Repeat with the other four buttons.

heretic
12-03-1999, 02:36 PM
Sheesh, what are they teaching the kids in school these days?

Search for:
+"car radio" +buttons -cgi -form -gui

or variations thereon.

Mr2001
12-03-1999, 05:13 PM
Interesting. When I read the OP, I figured Mr2001 just wanted to know how to set his radio, not the theory behind its operation.

That's what a lot of people think when I ask.. but no, I'm interested in the mechanism itself. Guess I'll have to find one at a junkyard and pull it apart.

NanoByte
12-04-1999, 03:41 AM
I remember, as a kid, the second-in-sequence family car, a '38 Chevy, had a radio that had station buttons that actuated an electric motor that drove the tuning capacitor different amounts, depending on which button was pushed. I can't quite remember, but I think there was a screw under each button that would adjust amount of motor travel it would cause, and hence the station that it would tune in. I never took it apart to see how the thing worked. I doubt, at that age, I would've understood what went on in it anyhow. The motor, coupled to the variable capacitor, must've balanced a bridge, one pair of arms of which must've been been, in the case of each station, a potentiometer adjusted by the screw under its button.

Ray (looping on a face-lock)

AzRaek
12-04-1999, 12:48 PM
You could program those buttons? I never knew! I just pushed the buttons, and found the closest good station.

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John Jacob Jingleheimer Schmidt. That's my name too.
Wait, no it isn't.