[HUMBLER]

I finally bought a 10ohm speaker for my 70 GTO and hooked it up. I'm getting sound for a second and then it fades out. Turn it off and back on, sound for a second and then it fades. Is the radio just shot, it's the original.

Thanks!

[engineer]

output power transistor is dead when hot.

[HUMBLER]

And, I don't suppose that is fixable right?

[Ben M.]

Perfectly fixable. Get a new transistor or even upgrade that transistor while you are in there. It's a rather common one, I don't have the part number or specifications needed handy though.

[HUMBLER]

Does that require soldering and to what level of difficulty is the swap? Is that definately it, not wiring, other possibilities? Also, where do I get one of those?

Thanks!

[69geeto]

It does require some soldering (Two wires), but is pretty easy to get to. From what you are saying, it does sound like the output transistor. The transistor removes vie one nut. I believe you will need to drop the heat sink fin too. That depends on the radio (AM, FM). I will have to dig up the output transistor number for you. The last one I bought was a replacement # and had a hard time finding it. No more Radio Shack for things like that. You have questions..... they have more questions
Stu

[HUMBLER]

Thanks so much, I'm going to check with my club and see if someone may have one or can get one. We have a guy that fixes these things so I'm sure he can hook me up!

[HUMBLER]

Any lead on where to locate the transistor would be greatly appreciated. I'm going to go check a local place here in town but not sure if it is even still there.

[george kujanski]

SInce you get sound for a short time, the output transistor is working, at least for that time, so I doubt if it's dead.

I think it may be more likely a electrolytic capacitor, given the age of the radio...these dry out over the years.

George

[HUMBLER]

Uh, ok. I guess at this point, I'm just wondering if I can find the parts or not...

[george kujanski]

Even if you can't find an exact replacement, the nature of electronics components is such that a defective part can be replaced with one that will work correctly. As Ben says a transistor, for example, can be replaced with a newer, better, type. Ii do it all the time.

Once the defective part/s are found, replacement is pretty easy.

George

[Greg Reid]

Originally Posted by george kujanski

SInce you get sound for a short time, the output transistor is working, at least for that time, so I doubt if it's dead.

I think it may be more likely a electrolytic capacitor, given the age of the radio...these dry out over the years.

George

That was my first thought after reading the symptom. The capacitors (due to their ages) also have a higher probability of failure than does the transistor.
The last '60s Delco radio I bought required almost every capacitor to be replaced. I didn't care about it being the same identical type, just the same capacity in farads, of equal or greater voltage rating and general application type. I had to get creative to fit them in but it wasn't anything too difficult.
Afterwards, it fired right up and worked like a charm.

One last point, the transistor can be checked by most any tech with a meter, to a reasonable degree of certainty. It takes a bit more know how and equipment to check a capacitor properly.

[HUMBLER]

Thanks to all and especially MERLOTGOAT, sounds as if I'm good to go.

[Dan968]

most the time, but not always a transistor will start to distort the sound when it is failing.
I would verify 12v and a good ground at the radio first.
As far as capcitors, if you do not have a capcitor checker try looking at the leads where they exit the capcitor. If they are corroded or have a greasey looking discharge, they are bad. In my shop, we find alot of bad capcitors just by looking at them before we even get the ESR meter out.
Dan

[HUMBLER]

Originally Posted by Dan968

I would verify 12v and a good ground at the radio first

I was wondering if that might have something to do with it, I'll ask merlotgoat about that as well...

[69geeto]

I have seen these transistors leak at they heat up. Great sound for a short time, then nothing. Does it get hot when the sound dies? If so, my money is still on the transistor. If not, a cap sounds good to me too!
Stu

[HUMBLER]

I'll give you the full run down once received from merlot...thanks again.

[HUMBLER]

Well, much better than thought..oh crap..merlot what was it? "Bias something" was set wrong... Didn't have to replace a thing!

[merlotgoat]

Bias adjutment pot was dirty/corroded, causing the output transistor collector voltage to be 3.4 volts instead of the normal 1.5 volts. Clean and readjust was all it needed. Other than that, radio is like new.

[HUMBLER]

Thanks again.