69 AM Radio - Smoked? - Team Camaro Tech
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post #1 of 7 (permalink) Old Jul 10th, 06, 02:07 PM Thread Starter
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Jonny
 
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Question 69 AM Radio - Smoked?

Was attempting to wire up a 69 AM stock radio in the camaro over the weekend I got off ebay for $11. Hooked up a power source and ground, and the lens light came on. OK so far. Hooked up the speakers and turned on to hear a soft *thump* as expected. So the speakers are working OK. Turned up the volume and no sound - but a good puff of smoke. UH oh! Maybe that's what I get for $11~!

Well I at least want to make sure I'm hooking this thing up right - it's my 1st time with an AM radio!

As I recall there are 5 connectors in the back, reading from left to right:

GROUND
PWR
LAMP (no connector)
SPEAKER
GROUND

I hooked up the left side GROUND to ground and the PWR to 12V. Lamp comes on. Hooked up (2) speakers in parallel with + to SPEAKER and - to the other GROUND. I got this hooked up right (considering it is a mono stereo?)?
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post #2 of 7 (permalink) Old Jul 10th, 06, 05:05 PM
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Re: 69 AM Radio - Smoked?

I would tend to think the older GM AM radio's could only have a single 8 ohm speaker connected to them unless they were designed for 2 or more speakers. From what I can see with the terminals on the radio it was only meant for one. I think you might have smoked the outputs or a resistor inside the unit.

The 2 speakers you had, were they 8 ohms ?. If so and they were wired in parallel then the load would have been 4 ohms which may have been to low and the radio was trying to put more power out than it could due to the lower reistance and smiked something. If you had 2-4 ohm speakers in parallel then the load would have been 2 ohms and that is definately too low.
At low volumes the radio should not care if the load is 2 ohms or 8 ohms but the louder you turn it up the more it's trying to put out and the lower resistances will have the outputs of the radio really trying to put out power to where if it's not designed to handle that low impedance/resistance things will go up in smoke, fuses may blow or on some newer style radio's they go into protection and not allow major damage to occur.

The reason for 2 grounds was one was for the radio while the other was for the speaker. Both are quite possibly to the same point inside the radio and it's what they called common ground outputs. Years ago you could run a positive wire to the speaker and then take the other terminal and ground it next to the speaker or it was attached to the speakers frame to where once it was mounted and grounded the speaker worked. Common ground outputs could only allow for so much output power while today's newer radios have floating ground outputs and no speaker wires can be to ground and this along with a different designed output stage allow for more power output.

Jim

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post #3 of 7 (permalink) Old Jul 10th, 06, 06:03 PM
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Re: 69 AM Radio - Smoked?

Puff of smoke? No bueno. If it fills the hole in the dash, it's worth 11 bucks though........
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post #4 of 7 (permalink) Old Jul 11th, 06, 10:28 AM Thread Starter
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Re: 69 AM Radio - Smoked?

Quote:
Originally Posted by kz1000ltd
Puff of smoke? No bueno. If it fills the hole in the dash, it's worth 11 bucks though........
My thoughts, exactly, kz. And that was my original intention - just to fill the factory hole in the dash!! Looks cool!

I thought I'd give it a try to see if it was actually a working unit, but yeah, forgot to think about the speaker load in parallel. Trying to remember by old electrical theory classes about loads in parallel and series. If I put the speakers in series, the radio should see the same load, no? I forget.

I'll try wiring up to a single speaker, but I got a feeling this one's **SMOKED!**
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post #5 of 7 (permalink) Old Jul 11th, 06, 12:01 PM
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Re: 69 AM Radio - Smoked?

Delco speakers were 10 ohm impedance and OE AM radios were designed for one speaker. By placing two 8 ohm speakers in parallel, made the total impedance 4 ohms, 2.5 times the load as designed.

The power transistors went "poof!" You might by able to unscrew the transistor from its socket and pry it out to take to an electronics shop for replacement. If you have to unsolder the emitter and base connections, use a max of 25 watt soldering pencil, not an iron.

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post #6 of 7 (permalink) Old Jul 11th, 06, 12:03 PM
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Re: 69 AM Radio - Smoked?

[QUOTE=The Beerboy]If I put the speakers in series, the radio should see the same load, no? I forget.

Series resistance adds. Get 2, 4 ohm speakers and hook them in series and you should be fine. I'm with everyone else. You'll never hear or want to hear a AM radio anyway over the sound of your beast.

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post #7 of 7 (permalink) Old Jul 13th, 06, 05:52 PM Thread Starter
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Re: 69 AM Radio - Smoked?

Haha, yeah I agree that the AM would suck to hear LOL

I actually have a master plan where I'm going to stick the face of a new (removeable faceplate) receiver in the console (under cover), that will remotely (via wires) operate the head unit located in glove box. This gives easy access to controls/volume and hides nicely from view - and looks like the AM radio is jamming! That will be a while before I get it hooked up, but I'll let you all know how I make out.
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