Problem With Radio

[RobW]

The latest chapter in my never ending radio saga in my 73 CDV. Originally had a am/fm wonderbar. Worked OK but drifted a little bit. Also had no stereo to the left even when trying to adjust balance. I had an old an/fm 8 track from a 74 or 75 deville. Can't remember exactly which year since I swapped it with a car we were selling at the shop about 30 years ago but I remember it having the newer dash. Anyway that one worked  good on tape but was a little staticy and also drifted a bit. Had that one repaired for somewhere around $300. Got it back and the tape was excellent. The stations were much clearer but had nothing below 92 FM and above about 105 FM. Would drift sometimes still.
The guy that repaired found me another used working am/fm 8track from a 73 and I've had that one in the car for about 10 months or so. This played well but also drifted a bit, but much better than the others. The tape player however is a bit noisy and the tapes that played well in the repaired radio sound terrible in this one.
Anyway, I took the car out yesterday to put my new tires/wheels on it and while driving it back to my house I lost 3 of the 4 speakers. All that is working now is front right side. So I thought maybe I hit a bump and knocked something loose. Couldn't find anything loose. So I tried the old wonderbar radio. Same thing only right front speaker, a slight static in the left rear. Then I remembered this radio didn't work on the left. Its a cross stereo system so right front/ left rear and left front/right rear play together. OK so I'm thinking let's try the repaired one and see what happens. Put that one in, and got 3 of the 4 speakers working. The right rear still doesn't work. Gave up for the night and figured I'd try again today to see if I can swap in a good speaker or trace out the line for a break somewhere. Car was only in the garage 2 days so I don't think any mice got in as I can't find any droppings or anything chewed up so far. Went back out now and it's only playing on the front right again!
Now I'm really confused! First I thought I lost the speaker circuit to rear. But then to have the same problem on 2 radios was a bit unlikely. But then that second radio didn't work to the left side so I thought OK bad rr speaker. Then the repaired radio worked everywhere but the right rear so that pretty much confirmed my theory. Now this one is doing the same as the first one.
Any ideas? Bad rear speakers? 3 worthless radios? Broken wire somewhere to the rear? I guess I'll start by tracing the wire to right rear and swapping a speaker there.
I know the real solution would be to join the 21st century and forget about these 8 track radios or wonder bar radios but I'd like to keep it original and I really don't want to add a radio under the seat or in the glove box or trunk.
How about you other guys with mid 1970's radios? How do yours work?

[RobW]

OK now I tried jumping out the right rear speaker and nothing. Tried another speaker and it works so bad right rear speaker.
The repaired radio started working after I slapped the bottom of the case. Guess something is loose inside? Expensive paperweight! LOL!
So now I'm thinking something inside the other 8 track went bad while I was driving it back home. Sound reasonable?
Anyone have any thoughts about repairing these radios? Parts still available? Or is it just a temporary "fix" and another waste of money?
Maybe I should just buy one of those "classic" radios made to fit the daash opening. I really hate to do that!

[TJ Hopland]

All my 70's radios seem to have the drifting problem.  I dont remember that problem when they were new but maybe I was not as critical back then.     I have a couple cars with the retro radios in them and they work fine.   I dont think they make a cadillac specific one but you should be able to find one that is close.  Most of them are the same basic box they just have a different face and knobs to match the rest of the car.  The older models were not very high quality units and they had some quirky features but from what I have seen more recently they look like good units.   A few years ago I took apart the radio in my 78.  I was not able to fix the 8 track which was fine since I dont have many tapes anyway but I was able to figure out how to add an I pod hookup.  I dont remember the details but it did work.

[Doug Houston]

If you can get someone to test the speakers individually, connecting  each one to some audio signal source, you'll find out a lot more about them than switching radios, as you've been doing. You could find open voice coils, or dried out speaker cones. Those need replacement. Your speakers could easily test OK.

Disconnect each speaker from the body harness, and connect some signal source to it.The speaker will show as either good or bad. I sort of suspect some problem in the output circuitry of your radio(s).

Since this is a closed car, it should be possible to use the later design 6X9 oval speakers in it, as there is enough space in the trunk for them. In many sets, the mounting of the original speaker won't accomodate a newer design speaker to be installed.

The radios have a front-rear  speaker control in them. It's a variable resistance, much like a volume control. If the radio has set for a long time, like a couple of years, the resistance wire on the control, or the contact arm for it can get oxidized, and make bad contact. That could be what's going on in your set.  If the speaker control is accessable with the set out of the car, find an electronic supplier (not easy today), and get a can of De-Ox-It spray contact cleaner, and spray it on the control, so that the stuff gets inside the control housing. Then, rotate the control a few times, to polish in the contacts between nthe resistance unit, and the contact arm.

There is a company named McMaster-Carr, that's a good source for a lot of electrical-electronic items. They have a web site.

Back years ago, I had a Cadillac set, from about this same era, that I mounted in a '71 Oldsmobile Custom Cruiser wagon. It worked very well, and I didn't have the problems that I see here. It was a pretty good set.

[Glen]

It seems the capacitors made back then did not last as well as the earlier ones.  As the capacitors go bad various circuits quit working right.  Most of these radios had a circuit called Automatic Frequency Control (AFC) that keeps the radio on station.  If the capacitors in that circuit go bad the radio will drift. 

A common fix for these old things is to change out all the capacitors.  Kind of labor intensive but you end up with a radio that works like it did when new. 

Glen

[RobW]

I have new 3 1/2" speakers in the front. Both work on the repaired radio where the guy says he swapped out many leaking and weak capacitors. Problem is it still drifts and the range of stations is much narrower. On the radio he gave me as a peace offering for my dissatisfaction with his repair, the range was from 87.7 to 107.9 FM. On the repair it was from about 92 to 105. Now that radio will play on 2 front and left rear speakers but when it heats up it sounds terrible and drifts so there's definately something wrong in there. The other one he gave me worked pretty good as a radio up until Friday when I lost one side of the speakers. So I think that's an internal radio problem.
I would like to get one of them fixed. I don't the one that was repaired is any good now that someone went through it and did alot of soldering on the circuit boards. The one he gave me I think has bad heads in the tape deck. Maybe between the two a good shop could make one? Then I have another I bought on ebay and received dented on one side and is barely audible. I finally got a refund through paypal as it was not as described. The seller stated it worked perfectly. It appears only the case is dented and nothing inside was hit. So that might be a good candidate for repair.
The original wonderbar is OK but it too lost one side. I think that could be repaired. Maybe bad rear speakers caused an internal problem? The service manual states not to power up the radios with speakers disconnected as the audio transmitter may be permantely damaged. So would connected but blown have the same effect?
Now the other problem is the repair sites I've found on the internet all start at $450 to repair either the wonderbar or the 8 track. I don't mind paying the $450 IF it works. But I'm not really convinced after the last go around. Some of the repairers seem a bit eccentric to say the least and would probably react like "the soup nazi" from seinfeld if there was a problem after the repair.
I"ll change both rear speakers since one is bad anyway. But I'm still not sure what to do about the radio? It's kind of pointless to keep trying used ebay radios that either don't work as described or have been sitting forever in who knows what conditions, dust, moisture, etc.

[Doug Houston]

I've been a radio collector since the early forties, and have serviced radios since a little after those days. The capacitors in a radio deteriorate with age, and with few exceptions, become (electrically) leaky, and need replacement.

I haven't done it on all of the collector sets I have (about 600), but when a set is re-capped, it's new, and when properly aligned, works as new.The capacitors we buy today have nbetter materials in them, and should out-live any of us.

Solid state (transistor) radios use what is known as electrolytic capacitors in many places where other styles had been used. Electrolytic caps deteriorate faster than the ones used in vacuum tube models. This is probably what is happening with the sets that are plaguing you.

There are exceptions of course, but I have some sets that were built in the mid-thirties, and which work almost as good as they did when new.

On the other side of that coin, Zenith brought out a fine portable AM-FM radio about 1960. I bought one new in 1962. A few years ago, it wouldn't work. Already some of the electrolytic caps had dried out.replacing them got the set going again like new.  So, whether or not the radio has been in use, may not mean that the capacitors have survived. My own '70 Convertible has been in storage for around 30 years, a distance from home. I'd be astonished if the radio worked.  I should un-bury the '72 (?) Cadillac set I had in the olds,and see if it works. The thing I'd worry about, if it works, is: for how long?

My '56 convertible is parked alongside the '70. If the vibrator will start (which it probably wouldn't), the radio will probably work decently. I once bought a spare '56 radio. A while back, I fired it up, not changing anything in it, and it works like a champ. Even the search tuner works. That's why I like vacuum tube radios!

It looks as though the speakers are working OK in this car, but that the circuitry in the set is giving the trouble. I know a guy in Ohio, North of Cincinnati, who MIGHT consent to looking at your set, but I'd ask him about it before I'd give his name to someone. I'd have him work on my radios, but solid state radios have tons of heartaches built into them. 

[RobW]

Thanks Doug. That sounds like a reasonable explanation. Do you really have 600 radios? So you think these can be repaired to work OK? Just a matter of finding the right place then?

[TJ Hopland]

Solid state amplifiers dont have a problem running with no load (no speakers hooked up).  Most tube designs dont like no load.

[Doug Houston]

I hate to barge in here so adamently, but NEVER, not EVER run a solid state amplifier with no speaker load.  transistors will be blown before you even have a clue to it. There have been some instances where I've had a speaker lead come loose, and the amplifier wasn't harmed, but as a rule, especially with a good signal coming from the amplifier, you will lose the output transistors.

Now, with vacuum tube circuits, if there is a strong signal going through, with no speaker load, you have a better chance of the thing surviving. I've seen output transformers blown from high level signal and no speakers. But vacuum tube equipment is somewhat forgiving, but not  so with transistor amps.

[RobW]

Doug
Maybe that's what happened when my right rear speaker went bad?

[cadillacs]

I worked for a Delco radio shop in the 70's here in Tampa. I remember the the early 70's Delco radios used "rivets" to connect the lands on the top of the circuit board to the lands on the bottom of the circuit boards. In this climate the "rivets" would lose connection causing the customer to loose one side or the other or maybe just FM, etc. Delco had a fix where you would install a jumper kit to replace the rivets. They had a fancy name for the repair that I don't recall. I doubt one could be located after all these years. Also GM cars before '77 used grounding speakers. The negative side of the speaker was grounded at the speaker...only one wire came from the radio on the rear speakers. If you replace the rear speakers with aftermarket you will need to ground the negative wire. Hope this helpful. Doc

[TJ Hopland]

I hate to barge in here so adamently, but NEVER, not EVER run a solid state amplifier with no speaker load.  transistors will be blown before you even have a clue to it. There have been some instances where I've had a speaker lead come loose, and the amplifier wasn't harmed, but as a rule, especially with a good signal coming from the amplifier, you will lose the output transistors.

Now, with vacuum tube circuits, if there is a strong signal going through, with no speaker load, you have a better chance of the thing surviving. I've seen output transformers blown from high level signal and no speakers. But vacuum tube equipment is somewhat forgiving, but not  so with transistor amps.

Doug, your experience is opposite mine.   I do admit that I have never worked with or carefully studded the design of car radios.  Do they use unique designs different from what you find in other markets?  Perhaps the lower power input voltage changes things?  Most of my experience and training is in 'pro' audio with a little consumer gear in the mix. With modern pro audio and consumer products it is very common to have channels not connected.   In the 80's many pro amplifiers were actually rated to have only one channel (of a typical 2 channel amp) connected.  Now days with switching power supplies being common they dont tend to do that anymore, most equipment can operate at full rating with both channels driven and into very low impedance.  I have seen stuff rated down to 1.2 ohms.  In the 80's you were lucky to get 4.  The issue in the tube amps I am familiar with running them with no load results in a shorted output transformer.  At the moment i cant find any documentation online to back my theories.  I will have to look later or go searching for my old textbooks.  I never got deep into amplifier repairs so most of what I learned is long forgotten from lack of use. If you have any info to back your theory please post it so I can be properly re-educated.   I do maintain a few tube systems and there are aspects of them that can take a ton of certain types of abuse that even a modern solid state amp would have issues with.  I have one system that has survived nearby lightning strikes that have taken out much of the other solid state gear in the building.   

[Doug Houston]

I probably have some articles that caution operating SS equipment sans speakers. The first place I'd look would be the instruction sheets for most solid state stereo equipment.I could probably look up even the Delco service sheets for our radios. I'm a bit surprised to hear that any equipment maker would condone speaker-less operation.

For allthe years that tube equipment was made, speakers always were emphasized to be connected, lest the output transformer fail from internal arcing. Not always, but with speakers disconnected, you're treading on thin ice.

[TJ Hopland]

The main tech guru guy I know has been stuck on jury duty all week so I have not been able to talk to him.  I did talk to another guy that has done some repairs for me that seems to know his stuff.  He said its all dependent on the design.  Tubes vs solid state does not in itself make any difference.   Many amps are designed to take a fairly wide range of loads so they dont tend to have issues with no load.   Typical consumer products that dont come with built in speakers or aftermarket things like car stereos should be designed that way because the designers dont know exactly what the user is going to connect.  This is why most people have never had a problem.   Something like a factory car stereo may not be designed for a range because in theory they are only going to have the factory speakers connected all the time.   

One reason many of us think tubes have the no load problem more than solid states amps is that in a tube amp you have a decent chance that one or more of the tubes is going to be weak.  A weak tube is going to change the design and performance of the amp.  Its very possible that a weak tube could make the amp prone to oscillation especially if its not working into an optimum load.  This oscillation in a tube amp often results in shorting the output transformer.  Output transformers tended to be custom made pieces for each model amp so that meant that even when tube amps were commonly used replacement transformers could have been difficult and or expensive especially on compact devices (like a car radio) where the physical size is as critical as the function.    Solid state amps could also suffer the same problem but dont use a output transformer and historically the components that could be damaged tended to be less expensive and more universal.   With modern chip based stuff we are back to the custom design stuff that is difficult to service but many of the designs now are much smarter and have internal limits and monitoring to prevent overloads and oscillations.  Any amplifier could have the capacitor issue that was mentioned in an earlier post.   A old/ bad capacitor just like a weak tube will change the design and performance of the amp which could lead to all sorts of problems.   

So as far as the original question goes it seems that it is possible that especially due to the age of the car in question one of the failures could have lead to the other.   

I also found out that everyone had an opinion on this question but almost no one (including me) had any real info to back it up.  Maybe we can send it in to Mythbusters and have them blow up a bunch of amps and speakers?