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Old 05-22-2019, 10:09 PM   #1
Markuli
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'67 AM Radio very quiet and static-y

I need some guidance here, guys.

Since I bought my truck, the radio would only make a faint "popping" noise when turned on, no music or anything. I tried turning on the radio just the other day, and it turned out that it no longer made any noises at all. When I finally pulled out the speaker and the radio, this is what I found:

- The speaker is trashed, as expected. Dry rotted through and the wires are cracked in the cone.
- My antenna cable was also chewed in half.
- The little coil that comes off of the antenna (inside the unit) was chewed off at both the antenna pickup and the solder joint it's supposed to wire into.

I re- soldered the coil in, plugged in a new antenna, hooked up two 4- ohm speakers to get an 8 ohm setup. Now upon bench- testing the system with a motorcycle battery as my power source, I have hardly any volume, and most of the AM range is static/ distorted. I can *just barely* pick up Mark Levin in the 700s range, that's about it

I'm trying to determine the root cause of my distorted signal and low volume. My questions are:

- I know I lost a "loop" or two in that antenna coil when I soldered it back in. How critical is it to have the proper amount of loops in that coil?

- I grounded my radio right to the negative of the battery... That's the best ground I can use, right? Would installing the radio in my truck give me a better ground?

- Is it possible that the transistor at the back is shot? That acts as the "amp" if my reading is correct...

-Am I completely bass-ackwards as to what to be checking out?

I'm sure we have some electronics gurus on here, so hopefully someone can steer me in the right direction!
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Old 05-23-2019, 12:08 PM   #2
Grumpy old man
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Re: '67 AM Radio very quiet and static-y

I was bench testing a few radios yesterday , I have one with the same issue and I was using a spare full size battery . I found pulling on the tuning R knob increased the volume slightly so I'm going to try some contact cleaner . another I set up worked great and the first station that tuned in was a local 70's rock station ! I sat and listened to it for a while when my girl walked in she looked at what I was doing and asked "Does it only play old rock songs ? "

There are GM am radio repair manuals on ebay
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Old 05-23-2019, 12:41 PM   #3
Markuli
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Re: '67 AM Radio very quiet and static-y

Haha! I was getting questions from my family about why I left the noise on as I continued researching, rather than turn it off... I was admiring the fruits of my labor!!

I actually read through some older manuals I found on the corvair forum. I don't think I'm adept enough to be trusted with a circuit board. There's a guy local to me who repairs AM car radios so I'll get a quote from him, but I'll probably end up buying another radio off the board here. Ya can't beat 50 bucks shipped. Even if I'm unlucky enough where the replacement doesn't work either, Mine is pretty gross aside from the face plate so it'll be nicer for the guy to work on.
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Old 05-26-2019, 06:31 PM   #4
Dead Parrot
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Re: '67 AM Radio very quiet and static-y

If that is a mostly untouched original radio, my suspicion is some/most of the capacitors are shot or real far off original specs. One link on the subject: https://antiqueradio.org/recap.htm

Also, if something was inside the unit chewing things, it probably took a piss or dump inside. Neither does a circuit board and parts much good. It also may have chewed something else. If you have one, examine what you can with a magnifying glass or similar.
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Old 05-29-2019, 07:38 AM   #5
Markuli
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Re: '67 AM Radio very quiet and static-y

Quote:
Originally Posted by Dead Parrot View Post
If that is a mostly untouched original radio, my suspicion is some/most of the capacitors are shot or real far off original specs. One link on the subject: https://antiqueradio.org/recap.htm

Also, if something was inside the unit chewing things, it probably took a piss or dump inside. Neither does a circuit board and parts much good. It also may have chewed something else. If you have one, examine what you can with a magnifying glass or similar.
The latter is definitely true, that radio was covered in mouse "evidence". Crap falling out of all the nooks and crannies... I took a read through that web page and it confirms what I also read in the troubleshooting section of the Corvair radio service manual (these radios share a lot of the same components and layouts). If I ever get around to testing the old radio it'll probably check out as the capacitors. Link for those interested: https://www.corvair.org/chapters/cor...anuals.php#RRM

I ended up buying a radio off the forum and it works like a charm. I've read that these radios are hard to kill, but the mice managed to send mine to its grave.

Now I have to decide if I want to spend the dough on an oem- pattern upgraded speaker or try and get these (surprisingly decent) Autozone speakers to fit without any cutting.
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