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Discussion Starter · #1 ·
I recently got a refurbished Delco AM/FM stereo to put into my 72. ( I believe it's actually a newer radio, maybe 73-74? Dimensionally the same as the 72.) Anyway, the car was originally am equipped. I need speakers for this radio and have heard I need 10ohm speakers and cannot use newer speakers as they are 4 ohm and I'll blow the output in the radio if I use 4 ohm speakers. I have a few quesions:
Can I somehow put a resistor in a newer speaker to give 10 ohm resistance?
If not where can I get 10 ohm speakers?
Lastly I was really hoping to add an Amp to this radio using a line output to RCA adapter and wiring it into the amp that way. Can I do this or does that go back to the whoe 10ohm VS 4ohm problem?
Is there any way to make the amp work with the old radio?
Thanks!
 

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Can't help with the amp question but if you need 10 ohm speakers try Antique Car Radio
Fred Cranshaw (owner)
1624 Bitter Creek - Garland, Tx 75040
(972) 494-4099
E-Mail [email protected]

As to changing 4 ohm to 10 ohm- This rating is not the same as simple resistance (R). Although it expressed as ohms is actually impedance (Z), which is a function of capacitive reactance and/or (in this case) inductive reactance. It is not practical to add series/parallel inductance to change the impedance of a speaker.
 

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Back on the subject of speakers. What I stuck in my 72 dash was a pair of speakers from OPG. They don't use the original bracket, just a bent piece of sheetmetal that's drilled for the original mounting holes. Not the greatest things but do make noise. The dash pad hides them.
 

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Discussion Starter · #5 ·
I used a pair of them on my 69. Like you said, due to the dash pad covering them up, looks are not a concern. I have a stereo dash pad in the 72 though, so I need 2 separate speakers and I am concerned about them being the correct resistance. I don't know if they are 4 or 10 ohm. My guess is that they are new 4 ohm speakers.
 

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If your're not looking for anything special I got a pair from JCW that are stock replacements only with a larger magnet. With the Monte dash(72) I had to grind a bit off the magnet on the driver side to make it fit but they sound fine to me.

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Ole Paint
 

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Here's the lo-down guys...

Yes, you never ever want to use 4 ohm speakers in the exact place of the factory speakers when dealing with the original radios. The germanium based output transistors will be over-burdened with current as a result of the lower impedance

You DO NOT have to use 10 ohm speakers. The factory used 10 ohms, but 8 ohm speakers will work fine. The bad news; 8 ohm speakers are now dinosaurs for automotive applications.

I HAVE A SOLUTION This will eventually be in RADIO TECH but you're lucky enough to get a sneak peak. My solution is the EASIEST OUT THERE HANDS DOWN!!!.

Go to Radio Shack, ask for (4) catalog # 271-120 8 ohm 20 Watt non-inductive ceramic resistors. By snipping one of the wires that lead to a speaker and splicing this resistor in series, you automatically form a current limiting resistor. NOW YOU CAN USE 4 ohm speakers. Again, for each 4 ohm speaker you have, cut one of the wires to it, and place the resistor in between the two halves of the cut wire (that's what series means!).

But Coppertop, doesn't that result in an unwanted voltage drop resulting in lower power dissipation at the speaker??

YES, but it's hardly noticable, only a few decibles difference as a result of the voltage drop. Trust me, I've had this idea on the bench with factory original radios, restored radios, etc, it sounds fine!! Besides, if you don't do something, be prepared to shell out $$$ for obsolete germanium output transistors and emitter resistors when you damage your output circuitry trying to drive 4 ohm speakers out of the box.

...And don't tell me the 17 year old at the car audio shop says I'm full of ********, I'm sure he has an in-depth understanding of electronics and vintage Delco circuitry design...

Hope that helps.

Joe
 

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Discussion Starter · #8 ·
That's exactly what I needed to know. Thanks!
Now riddle me this: Is there any way to use that Amp I mentioned? That way I can get kick butt sound from my factory low wattage radio? I did this to my 78 Z28 when I was a kid until I could get enough money for a good reciever and it was great. Had it hooked to a pair if 6x9 rear deck speakers and man was it loud!
PS: The 17 year old at the local audio store says I need a pair of 12" powered subs and a bitchin' neon light kit.


[This message has been edited by Noneck (edited 04-11-2002).]

[This message has been edited by Noneck (edited 04-11-2002).]
 

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Noneck,

I can't really answer your amp question as I don't the know the input impedance of the amp. If it is a typical high Z (high impedance) that might be bad for the delco as it will look almost like an "open". For that case, you'd be best playing it safe connecting the 8 ohm resistors (I described above) directly in place of the rear speakers (dummy speaker loads). Then take the amp's input wires, and connect those across the resistor. (Parallel). But that's only if it's set-up how I think it is (the amp).
Can't say for sure without information.

Ya know...a properly functioning original radio isn't that "quiet" as most people think without aids of amps.
 

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Joe your idea is great on paper. However, the problem is heat not function. It works only at low volume. At higher outputs, which a lot of these guys run things, the resistor does get hot. A 20 watt amp into a 75 watt resistor gets it quite hot over time. The resistor doen't fail, but it's too warm to put under a dash. I've done what you have described.
The idea may work better using a certain length/gage of resistance wire to one side of the speaker. You won't have the concentrated hot spot.
 

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John,

Don't want to get in an argument, these get "warm" at most. I've tested this on the bench with FM rock stations blaring away for hours. The resistors I provided the part #'s to have a 20 watt rating. They'll easily dissipate the power with melt-down.

[EDIT]

John, you misunderstood, these are NOT to be used with AMPS, only with the factory radio's in their original output form! The factory radios only had about 1 to 2 watts output.

Joe

[This message has been edited by Coppertop (edited 04-11-2002).]
 

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Joe
You know me. I don't argue with you, but I've got you to clarify things. This subject has come up before. Didn't want anyone to read this later on and say
"Coppertop said it was OK to add resistors and now something under the dash is burnt and the amp is a mess."
 

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I know you don't


Good call John, clarification was a good idea, someone might have tried that with amp connections.
 

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I also don’t want to argue but rather would like to think this is discussion. I’m having difficulty understanding how when adding five times the resistance in series with the speaker you don’t lose most of the power across the it. Wouldn’t you get better sound quality by using the correct speakers? Especially considering the low power output if the factory radio.
 

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<BLOCKQUOTE>quote:</font><HR>Originally posted by Elree Colby:
I also don’t want to argue but rather would like to think this is discussion. I’m having difficulty understanding how when adding five times the resistance in series with the speaker you don’t lose most of the power across the it. Wouldn’t you get better sound quality by using the correct speakers? Especially considering the low power output if the factory radio.<HR></BLOCKQUOTE>

Elree
Joe's not suggesting 5 times the impedance, only a 4 ohm, 20 watt resistor. Yes there is a loss across it. This is a band-aid fix if you can't find the right stuff.
 

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Discussion Starter · #17 ·
Thanks so much guys! What ever would I do without this site? (Other than smoke a perfectly good radio!) I think for now I'll do as Coppertop suggested and try it without the amp. If I really can't stand it, I'll give you a yell! (Although I almost don;t miss the radio anyhow as I'm always listening to the big block!) Thanks again!
 

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OK 20 wattsnot 20 ohms. Even at 8 ohms two times the speaker resistance the resistor will dissapate most of the output power.
 
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