[2002Z4CSS]

I purchased a reconditioned Delco AM radio for my 1971 GT-37 from ebay. The radio and the knobs looks like brand new and used to work like new. Now the radio cannot be heard unless the volume is turned all the way up and you can barely hear it. What do you think happened to it? The biggest thing is this radio has not seen more than 1 hour of play time since it was installed due to engine problems and the car just sat for almost a year.

[russosborne]

Odds are a power amp is blown inside of it.
Check all the connections and grounds just in case it is something simple though.
Reconditioned means different things to different people. Hard to know what was actually done to it by the reconditioner.
Did you get any sort of warranty that is still good? Unlikely I know, but maybe you did.
Russ

[sts]

Dee odds are even better that it's a mismatched ohm issue between the speakers and raido.

[steve v]

The factory radios usually use an 8 - 10 ohm speaker.

[68bird400HO]

Originally Posted by 2002Z4CSS

I purchased a reconditioned Delco AM radio for my 1971 GT-37 from ebay. The radio and the knobs looks like brand new and used to work like new. Now the radio cannot be heard unless the volume is turned all the way up and you can barely hear it. What do you think happened to it? The biggest thing is this radio has not seen more than 1 hour of play time since it was installed due to engine problems and the car just sat for almost a year.

1) Check for corroded contacts, esp to speaker.
2) Check antenna connection.
3) Check your speaker cone for tears.
4) Make sure you have an 8-10 ohm speaker as already suggested.
5) Lastly, and most likely, you need to adjust your antenna trim with the little screw in the little hole above the tuning knob. Here is a good thread from V8Buick.com on a few radio adjustments.

http://70.86.163.37/showthread.php?t=222637

[stevep]

Try a known good correct speaker.

[2002Z4CSS]

Thanks guys. I will try a good known speaker if I have one. The one in the dash is a GM speaker but I think it is a 4 ohm I had laying around. Can more than one 4 ohm speaker be used if I don't have an 8 ohm speaker?

[russosborne]

Ah, I was assuming you had the stock speakers, I knew I should have asked.

Did it work ok with the same speaker before? Depending on the quality of parts, you can blow the output amp quickly by using the wrong ohm speaker. Hopefully that isn't your problem.

and yes, if you add two 4ohm speakers in series you get 8ohms. Radio out to proper side of first speaker, then other side to opposite of second, then last connector to radio. Radio neg to speaker 1neg, speaker 1plus to speaker 2neg, then speaker 2plus to radio plus.

If you were to connect them plus to plus and neg to neg they would be in parallel, which would give you 2 ohms total. Not good.

And yes, I am an electronic technician in real life. :-) Mainly deal with RF stuff though.

Russ

[69geeto]

I have seen the bias pot get dirty and kill most of the sound at the output transistor. I'm not sure where it is located out the back of the radio but it's a small adjustment Philips head variable resistor. You might try just turning it very lightly back and forth. And as mentioned earlier, 4 ohm speakers are not going to help the life of your output transistor.
Stu
Motorola eng.

[2002Z4CSS]

I hope to check it out today if the rain stops. I hope I did not waste $150 on a AM radio.

[68bird400HO]

Originally Posted by 2002Z4CSS

I hope to check it out today if the rain stops. I hope I did not waste $150 on a AM radio.

I think you are fine. It is pretty tough to kill these old radios. I had the exact same problem with the AM in my '68 bird and IIRC the antenna trim adjustment fixed it. Now it is loud and clear.

[2002Z4CSS]

Originally Posted by 69geeto

I have seen the bias pot get dirty and kill most of the sound at the output transistor. I'm not sure where it is located out the back of the radio but it's a small adjustment Philips head variable resistor. You might try just turning it very lightly back and forth. And as mentioned earlier, 4 ohm speakers are not going to help the life of your output transistor.
Stu
Motorola eng.

Do you have a picture of this part?

[69geeto]

On this radio towards the bottom right of the picture you will see a recessed Phillips type adjustment. Gist rock it slightly and see if that helps. I would use a plastic adjustment tool if you have one. Good luck!!
Stu

[2002Z4CSS]

Originally Posted by 69geeto

On this radio towards the bottom right of the picture you will see a recessed Phillips type adjustment. Gist rock it slightly and see if that helps. I would use a plastic adjustment tool if you have one. Good luck!!
Stu

Thanks! If I don't have anything plastic to turn that what would you recommend?

[69geeto]

Maybe a small Phillips. I don't remember the makeup of that pot, but just rock it a little bit and don't touch the screw driver to the metal case. Just being overly cautious
Stu

[2002Z4CSS]

Originally Posted by 69geeto

Maybe a small Phillips. I don't remember the makeup of that pot, but just rock it a little bit and don't touch the screw driver to the metal case. Just being overly cautious
Stu

Thanks again.

[2002Z4CSS]

Originally Posted by 68bird400HO

I think you are fine. It is pretty tough to kill these old radios. I had the exact same problem with the AM in my '68 bird and IIRC the antenna trim adjustment fixed it. Now it is loud and clear.

I did not have tome to pull the radio out yet. Are you saying if I used the wrong ohm speakers and get an 8 ohm speaker or two 4 ohm speakers in series, the radio may play fine again without hurting any transistors?

[GT182]

Yeah, the wrong ohm speaker could be the cause. The catalogs say a 4 ohm total impedance with these old radios. But the antenna trim adjustment could help too. Use the weakest station you get to adjust the antenna.

[j69shep]

Most likely you have a radio that has multiple problems, starting with the audio section. Low volume could be a problem with the preamp section or the main output transistor and associated circuitry itself. If you had an incorrect speaker and a working radio you would still get plenty of sound, just not for too long. With a radio that old you need to re-cap it first to get the power supplies to work correctly. Bad 40 year old caps in your power supply circuit will affect everything. I have fixed hundreds of them and I change all the caps first and then fix the rest of the radio. Of course to change out all those caps you should be able to desolder and solder in the new ones correctly as some are polarized. Send it to me and I'll get it playing in no time. Regards, Jim

[2002Z4CSS]

Originally Posted by j69shep

Most likely you have a radio that has multiple problems, starting with the audio section. Low volume could be a problem with the preamp section or the main output transistor and associated circuitry itself. If you had an incorrect speaker and a working radio you would still get plenty of sound, just not for too long. With a radio that old you need to re-cap it first to get the power supplies to work correctly. Bad 40 year old caps in your power supply circuit will affect everything. I have fixed hundreds of them and I change all the caps first and then fix the rest of the radio. Of course to change out all those caps you should be able to desolder and solder in the new ones correctly as some are polarized. Send it to me and I'll get it playing in no time. Regards, Jim

Shoot me a PM with the details. I would like to get the radio working. At least then I could get an FM convertor.