am/fm singles, some strong, some weak - Team Camaro Tech
Electrical & Wiring Troubleshooting electrical.

 
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post #1 of 9 (permalink) Old Oct 11th, 04, 05:33 PM Thread Starter
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Location: Dallas, Texas
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I live in Dallas,Tx. I have an original am/fm radio in my 67. There are several MAJOR radio stations around town. For some reason, some station come in nice & strong & clear, while others are really hard to bring in. Isn't there some kind of "fine tunig" one can do with a screwdriver on these old time radio(s). Thanks for any suggestions ya'll.
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post #2 of 9 (permalink) Old Oct 11th, 04, 07:55 PM
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To align a radio takes special equipment. There are several tweakables in there. But if you mess with them without the proper equipment you are asking for trouble. You can't just tune for the best signal.

Also, beware that radio technology has come a long way in 30 years. For one thing, transistors were new back in the late 60s. Now days, low noise components and integrated reciever blocks have greatly improved sensitivity and selectivity. One problem that is common amoung radio recievers is desensitizing. This occurrs when a strong radio signal swamps the input stage of the radio reducing it's sensativity. So the station you're tuned to comes in poorly due to a strong station up or down the dial a ways.

Why do I say all this? Because you may be spoiled by modern technology. By today's standards, I'm not sure how well a 1960's era radio will perform.

Dave
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68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
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post #3 of 9 (permalink) Old Oct 12th, 04, 01:28 AM
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There used to be signal amplifier kinds of gizmo's that you could put inline to the antenna... These usually turned out to be noise amplifiers, but would help some with signals that needed just a little bit of boost ... Do make sure that the antenna cable connections , both ends, are intact and pushed all the way into the radio receptacle...
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post #4 of 9 (permalink) Old Oct 12th, 04, 08:38 AM
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The Dallas area has no shortage of strong signals. An attenuator is more likely to improve performance than an amplifier. That is because an amplifier would increase the desensitizing affect. Even if you were trying to pick up a weak FM signal from outside the area, all the strong signals in the area would swamp the input stage. Tuning doesn't happen until the IF stage. The RF stage (the one connected to the antenna) sees a broad band of radio signals which may include signals outside the FM radio band. All those signals over-load the RF amplifier much the same as an audio amp is overloaded in a noisey environment. The eye-in-the-sky helicoptor microphone is an example. The RF stage is the limiting factor. Ampliers work better in rural areas that are relatively free of strong RF signals in or around the FM radio band. But as you said sdtsdt, they amplify the noise as well as the signal.

Dave
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post #5 of 9 (permalink) Old Oct 12th, 04, 11:03 AM
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Steven
 
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I should have worded my response better ... I do not mean to recommend a signal amplifier. I was just having a senior moment ... The comments about noise amplification were intended to be a reason to stay away from these gizmo's as I called them . But, I did want to say that is check the antenna, particarly the "male" end that plugs into the radio. If it has been plugged/unplugged a few times ( and more so if it is an 30 yr + antenna ) underlying wiring may be damaged or disintergrating and conductivity may be marginal. Lastly, this radio is not digitally tuned. Fine tuning is done by how well you can minutely turn the knob as you listen to the station coming in. And, once you get a station just right, DON'T MOVE THE CAR !
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post #6 of 9 (permalink) Old Oct 12th, 04, 05:18 PM Thread Starter
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Hey Denult, is this "attenuator" something I could easily add on to my radio like an inline antenna signal booster? Is this something I would pick up at a Radio Shack? I have a new fm antenna & I've cleaned the female input to the radio. I'm sure it is all the way in & tight fitting. Do you think it would do any good to replace the "jumper plug." Looks kind of like a small vacuum tube. A guy on the internet sells them for old Delco radios for about $30.00. I haven't called him & talked to him yet. I don't know what in the world the thing really is or does. www.antiqueautoradio.com
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post #7 of 9 (permalink) Old Oct 13th, 04, 04:38 PM
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I'm not sure what the jumper plug is for, at least as far as your radio is concerned. Most likely it is exactly as it says - a jumper which probably wouldn't affect performance.

If it's really acting like a dud, consider sending it to a refurbisher. A few have been mentioned here in the past.

Dave
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68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
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post #8 of 9 (permalink) Old Oct 14th, 04, 05:43 AM
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The jumper plug connects the output amplifier section of the radio to the signal from the radio electronics. The radio will not work without that plug inplace unless you have a multiplex unit. The multiplex unit cable replaces the jumper plug with the cable connector. The multiplex unit splits the mono FM signal into 4 parts and then returns it to the output section of the AM/FM Stereo radio which of course has 4 output amplifier connections instead of the 1 the mono radios have.

Theres a signal adjustment pot (antenna trimmer)just above the tuning knob (right side). If you pull the knob and the dummy fader knob off the shaft you can see it just above the tuning shaft. Without signal generators to set the AM and FM modulators this is about the only adjustment you can make.

Mark Canning
1969 Indy Pace Car
350/300HP RPO Z11

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post #9 of 9 (permalink) Old Nov 11th, 04, 09:07 AM
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Joe
 
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Replacing the jumper plug wont help. If your radio had a multiplex it would send the tuner signal to the multiplex (through the connector your jumper is plugged into). The multiplex seperates the signal into channels and sends one channels signal back to the radios internal amp (again through the same connector your jumper plug is in). If you dont have the multiplex you have to use the jumper (which only contains a few resistors and capacitors) to connect the radio signal to the units internal amp. IT HAS NO EFFECT ON THE RADIO SIGNAL STRENGTH!

Do not start adjusting anyhting with a screw driver... you will make it alot worse. You need a service manual, signal generator and oscilliscope to adjust the radio.

Check that your antenna is good. If you are sure it is then you may need internal work on the radio. It is very common for these radios to have dried out electrolytic capacitors which cause all kinds of problems from Signal strength to audio noise and power problems. Any radio restoration shop can replace the caps and tune the radio for you.

Although it is possible that your radio is swamped with stronger signals as mentioned above, you can check it easily if you have some friends with older cars. Find someone with a delco am/fm radio approximately the same year as yours, in the same area and see if that radio tunes in more stations. If it does, then you have an antenna or radio problem.

The small antenna adjustment screw (trimmer cap) mentioned is for adjusting AM radio reception and does not have much effect on FM.


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