pwsusi

Took out an old broken aftermarket 8-track out of my '71 and installed an original '71 radio (mono) that i bought on ebay. I bought the radio only as the car still has the original convector and speakers. Hooked up the radio and sound is only coming from one speaker (driver's side). Since this is the first time i'm hearing any sound in the car (8track i removed was broken), i'm not sure if there's an issue with the radio i bought, the wiring, the convector or the speakers. I haven't pulled the dash out, but did lay upside down and looked up underneath the dash. From what i could see the wiring all appears to be in-tact, and the connection to the dead speaker seems to be fine. Any idea as to what the problem is and how best to diagnose?

Paul

Nowhere Man

a mono radio only uses one speaker. if your car has two speakers then your car had a stereo radio

pwsusi

Really? I was looking at this diagram and it appears as though even mono radios had two speakers. The diagram is for a '72 but i think the same would apply to a '71
http://forums.corvetteforum.com/c3-g...questions.html

Nowhere Man

could be I never worked on one I was only thinking that. I guess I was wrong. good luck

Jerry - Radio Guy

The passenger side speaker has an open voice coil Paul. It's extremely common. Place an ohm meter/continuity tester on the green and black wires going to the bad speaker and you will find an open path. The spot where the voice coil wire is broken will be under one of the strips of black liquid tape type material on the front of the speaker. It gets brittle and all the speaker flexing finally snaps it as it's very thin.

My understanding is that your Chevy parts dealer cannot get the original or either of the two substitutes as of a couple months ago. You can try aftermarket types but be sure they are 8 ohm units (Delco's 10 ohm is the same as 8 ohms due to the way they measured the reactive load).

Just send it in to have it re-coned. Actually, I'd send them both in and be done with it for many years. It takes about 2 weeks for the shops to rebuild them.

Another test you can make is to place your voltmeter across the green and black wires with everything hooked up. With two mono speakers in parallel you should read very close to 1.25 volts DC Paul. If one speaker is open, you'll read close to 1.5 volts.

Another point to tap in to read the voltge is to put the black lead on the radio case and touch the red lead to the center of the DS-501 round silver transistor that's mounted on your convector. That's the feed point for the green wire to both speakers. One last thing, if you're not getting very close to those readings, corrosion in the bias circuit of the radio (or aged electrolytic capacitors in the audio section) has occurred. That's common too and usually distorts any sound you get.

I hope that helps Paul.

_Jerry_

pwsusi

Thanks for the detailed information Jerry I appreciate it. I'm going to be taking the interior apart in a couple of weeks to replace the carpet, center console, bezel, etc... so it will be a good time to do the radio work. I will report back if i have any questions.

One thing you said that concerns me is about the 10 ohm speakers. While i was tinkering with the '71's radio, i decided to look stick my head under the dash of my other car (a '72). I noticed the '72 had aftermarket replacement speakers that are 4 ohms that a previous owner must have put in. I heard 4 ohm speakers could damage the radio, is this correct? The '72 has an original Delco mono radio also that is current working....sound is coming from both speakers but afraid i should be taking some action if the speakers are not correct.

Thanks,
Paul

Alan 71

Hi Jerry,
As I read the thread I was thinking of you. And then, there you were!
Yes, it's still working just fine.
Regards,
Alan

7T1vette

The mono radio has two speakers, just like the stereo units. But the speakers get the same signal with the mono radio. Since you are getting sound out of one speaker, the convector is 'good'. Your problem is either the speaker or the wiring. If you can reach the connectors hooked to the speaker wiring, see if you can 'swap' those connectors for the right and left side. If they aren't long enough, make some patch cables to get the job done. Fire up the radio. If the sound changes to the other speaker, then your wiring is the problem; I would be looking at the signal wires going from the radio head to the convector and back to the radio. If the sound comes out the same speaker (and none out the 'bad' one), the wiring between the connectors and the speaker is bad or the speaker itself is defective. If the sound now comes out both speakers , scratch your head, then button it up....that's want you wanted it to do.

jnb5101

wire the 4 ohm speakers is series. i bought speakers at advance auto for $10 each, and considering the sound quality the radio actually produces, they're loud enough to drown out all the other noises the car makes!

Jerry - Radio Guy

Ah, I see the forum has been restored after the successful hack attempt. So, I'll paste what I couldn't send earlier. Also, I see JNB has confirmed that the 4 ohm units in series works.
_________________________
First, Alan - HI and good to hear it's still working. Long may it play! Just keep snow out of it. It's sunny and nice down here y'all.

Paul, yes - 4 ohm speakers will put a strain on the DS-501 output transistor and eventually it will degrade and fail. Two 4 ohm speakers wired in parallel on the mono radio is the same as a single two ohm speaker. But, if you think about what I just said and twist it, two 4 ohm speakers wired in series are effectively 8 ohms and the radio would love that. So, with a mono radio, you can safely use two four ohm aftermarket speakers and the radio will be happy.

And, before this becomes too confusing, the radio can very easily be adjusted internally to handle just about any combination of speaker impedance's (and even extra 6X9 rear speakers for a fuller sound). The downside is that the same amount of power is being distributed across more speakers. And finally, the lucky guys with stereo 68-72 radios have two separate amps to drive speakers and there's way more power available to be creative.

It's really a shame that GM downsized to 4X6 speakers. They're fine for talk radio (bleh) but barely adequate for music.

When you get to the point that you're ready to address the speaker situation, drop me an email and I'll draw up a wiring diagram for two 4 ohm units in series if you're not sure how to do that. It's easy. No sense throwing away two good speakers in the 72.

One last item, if the radios do not sound good and you're sure the speakers do not consist of sun bleached raggedy paper cone remnants, then the electrolytic capacitors on the audio amplifier boards are failing. They were never intended to last for 40 years. The improvement in quality by just changing them (and a couple others) can be staggering (but a Bose it will never be).

Good luck with your project Paul! The older radios can sound good.

pwsusi

Thanks guys this is great info. Jerry, i'm going to take you up on that wiring diagram for the '72 to see if i can wire it in series and keep speakers I've already got. I have noticed lately the radio seems to cut in and out sometimes...I'm hoping damage hasn't already been done....hoping just a loose connection or something..have to take everything apart and check it out.

7T1vette

Series wiring: + speaker wire [from radio/amp] to + terminal on first speaker; jumper wire from - terminal on first speaker to + terminal on second speaker; wire from - terminal on second speaker to - connection to amp/radio. That's all there is to it.

Easy Mike

Check the options section of the AIM; it should show speaker wiring.

7T1vette

It does, Mike...but he is putting two speakers on each side and needs to know how to wire them together.

Easy Mike

Gotcha. I thought he was reinstalling the old stock system. Plus I was under caffeinated at the time.

jnb5101

i've got a speaker in the upper dash and kick on each side with a mono radio. wire each side's speakers in series, and each group in parallel. that is, run the output of the radio to each side.

pwsusi

Thanks guys. I'm all set with my '72 as far as wiring the speakers in series. As far as the '71 with one side not working....

I pulled the front dash pad and was able to diagnose the problem; the speaker is junk. Went to a few stores looking for a replacement and most were 4 ohm speakers. Rather than buy two new 4 ohm speakers and run them in series like i did on the '72, i was hoping i could just find one 8 or 10 ohm speaker to replace the dead one. I ended up finding one at autozone (metra aw-646sp) and it says it's 4-8 ohm compatible. I'm assuming this is ok to run in parallel with the original 10 ohm speaker on the opposite side? Hooked it up and it works, just don't want to do any damage. What do you think?

7T1vette

Set the balance control to the middle and the bass control all the way to 'treble'. Then set the volume at a normal hearing level and judge if the "new" speaker is much louder than the other (stock) one. If it is significantly louder, then the actual impedence is lower than stock and is drawing more current than the other speaker. You can adjust your balance control to compensate, of course; but if you turn the volume up toward the limit of the radio amp, there is a risk of frying the output transistor on the convector. Just keep the volume down to acceptable levels and you should be OK.