: No sound from radio, 1970 Sedan DeVille

09-18-08, 01:31 PM
Recently purchased a new-to-me 1970 Sedan DeVille. The stock radio lights up when the knob is turned on, and the radio can find stations when seeking, but there is absolutely no sound, no static or anything. Is this a common problem that is easy to fix? or do I need a new radio?

09-18-08, 02:02 PM
This car has 2 speakers, right? if so, plug in another known good speaker to the rear one's wiring and rotate the fader knob on the radio. 1970 speaker could be completely shot.

09-18-08, 05:06 PM
There are 4 speakers, 2 front, 2 back. I believe the rear speakers are the old grounded-to-the-car style (only one wire going to each). I have played with changing the balance and fader knobs but nothing changed. It is possible that all four speakers are shot, but I would expect to get something. If a detach the leads to one of the speakers, could I hook up a voltmeter? Does the radio put out enough voltage to each speaker to register?

09-18-08, 05:41 PM
Use an OHM meter not a volt meter. Also GM cars using a floating ground, so, no, they're not grounded to the body.

04-26-09, 03:32 PM
Can you elaborate on the floating ground? Can modern speakers be used with the old single-wire? I just bought a 1972 Sedan, and I have a similar problem to the original poster. My original factory radio lights up, but if I turn the volume all the way up, only a tiny amount of sound is produced. I was going to just try out some working 6X9s in the rear to see if I could get some sound, but don't know if the old single-wire style will work with the modern-style speakers.

04-26-09, 03:41 PM
Newer speakers work fine. Floating ground means the speakers are grounded within the radio, not to the body.

04-26-09, 04:54 PM
Swapping out the rear 6x9s will tell you right off if it's the radio or the speakers. It wouldn't surprise me that the speakers would be shot after all this time. Also, 1970 Cadillacs have the antenna integrated into the windshield, so make sure that's connected and not broken. Make sure all the connections coming of the radio are tight. I'll check the diagnostic tree when I get home for other ideas.

04-28-09, 01:09 AM
Thanks, guys. I tried hooking up a new 6X9. Just plugged the single wire into the + terminal on the new speaker - no sound. I don't have to ground the negative side, right? The wiring diagram shows a little ground wire, but I guess that may just be the representation of a floating ground. My '69 radio diagnosis chart basically has two options - "bad ground" or "antenna open or shorted", so the antenna's a good thing to check that I hadn't really thought about. My '69 manual doesn't cover the antenna-in-the-windshield, so I am waiting on a '72 manual off ebay before I go tearing stuff apart. I was starting to think I may have a bad amplifier, because all of the speakers, including front, are just really really weak.

Anyway, was I correct to simply hook the single wire up to the + terminal on the new 6X9?

Thanks again,

04-28-09, 12:45 PM
There should be two wires off the speaker IIRC, both go back to the radio. One is the input and one grounds the speaker in the radio. Also, the amplifier is a good thing to check. In 69, it's separate from the stereo radio. Not sure about 72.

04-29-09, 07:48 PM
I had the same problem with my '77. There could be a few problems: Im guessing the stock speakers are completely shot and need to be replaced, but if your using the stock head unit it most likely doesn't have enough power to make your speaks work. What you should try is replace the front 2 speaks and see if they work. If not you should consider a new head unit and with that said you will probably have to rewire your car unless you want to get an amp. I've done this all so if you need any help just shoot me a PM and we'll see what we can do

05-01-09, 11:47 PM
The output transistors are probably shot in the radio. It's a good radio for a vintage car. Take it and have it repaired. Upgrade the speakers and enjoy driving a classic car. That radio when it was new was way ahead of it's time.

The radio has more than enough power to drive any speaker. The originals work best though, because they are very high sensitivity.

Only upgrade to an ugly head unit if you really can't stand the sound of the old one.

05-19-09, 06:56 PM
OK, dash is torn apart. No sound from any speakers at all, but faint sound coming from the head unit itself. Does that indicate a particular problem? I've tried hooking up new speakers with no luck. Also, the '72 does not have a separate amp. The wiring diagram in my manual says that only one wire is connected to each of the rear speakers. I do not get that part at all, but that's what it seems to say. The antenna appears to be hooked up fine. The ground seems good on the exterior. I haven't taken the radio out of the car yet to open it up and see if the ground is bad inside or something.

Soon I will be trying to find someone that works on these old radios, if anyone can make a suggestion as to who is a reputable online repair shop, I would appreciate it.

05-20-09, 04:24 PM
I found this quote
Many replacement speakers now sold by the discount stores, auto parts stores and mail order restoration parts houses are labeled as "4 to 8 ohm compatible" and are in fact 4 ohm speakers. These speakers can damage the older transistor radios. 4 ohm speakers will measure around 3.2 ohms with a DC ohmmeter. An 8 - 10 ohm speaker will measure around 7.4 ohms with a DC ohmmeter. The DC resistance is the critical number for the Delco radios as the output transistor is in series with the speaker. A properly operating Delco radio should have 1.5 volts DC across the speaker voice coil. A 4 ohm speaker will draw twice the current of an 8 ohm and cause the amplifier transistor (the half dollar size device mounted to the black finned heat sink) to run very hot. The speaker cone should be displaced in an upward (away from the magnet) direction about 1/8" when a Delco radio is turned on. If the cone moves down toward the magnet, the speaker leads need to be reversed. Ford and Chrysler radios of the period used the same type of germanium output transistors as the Delco radios and also require 8 ohm speakers. However, Ford and Chrysler radios ran with 0 to 1 volt DC offset on the speaker depending on the radio model and vintage. Many will not deflect the cone when turned on like the Delco radios.

from this site


05-20-09, 07:55 PM
Thanks, Sled! Looks like a good site that I hadn't found yet. I've been googling like crazy, but can't find a diagnosis based on my problem - sound from the head unit itself, but nothing from the speakers. Well, now I know someone that can maybe restore this thing for $400. It's important to me that it looks original, as akimball said. So once I figure this thing out, now I have a source for repro 8V speakers.

05-20-09, 09:14 PM
your speakers need a negative and positive connection, which side are you connecting your one wire to? If you can't get those wires to work my suggestion is this: buy some 14-18 gauge speaker wire and run the wires from your trunk to the head unit under the carpet, then connect them to the head unit with a butt splice, it's real easy to do and you will have reliable wiring and it will power your speakers nicely. You'll also be able to know if your head unit a working properly. If you want to do this just post and I'll post pictures of what to do