Help with distortion in a Realistic 12-1290 AM radio
 

I have two of these Realistic 12-1290 AM radios, one of which I used to carry around in my pocket back in Jr High School. Both of them have distorted sound which I would like to repair. I believe with my own unit (that I bought new in the early '70's) that it has become worse with time (so I assume that happened to the other, also). Said distortion is linear and unaffected by volume level. You can hardly understand spoken words, it's so bad.

Anyone with experience with this? Does it sound like a capacitor or a transistor has "dried up" with age? There IS a schematic inside the back cover that I might be able to enlarge with Photoshop. Yeah, I know it's not worth a dollar three eighty- it's the sentimental value that counts.

http://i262.photobucket.com/albums/i...storradio2.jpg

http://i262.photobucket.com/albums/i...storradio1.jpg

I see three electrolytic caps that I'd consider replacing. Be sure to use the same values (voltage ratings can be higher).

Before you do anything check that the speaker voice coil is not rubbing on the magnet pole piece. With test leads, take the output of a properly operating transistor radio and clip it onto the speaker terminals of your Realistic. If it's still distorted, the speaker is rubbing. Replacement speakers of all sizes and flavors are available from Mouser.
Reece

Thank you both for your leads. I haven't had a chance to get back into these radios but didn't want you guys to think your ideas went in vain, either. I'll keep you informed. Thanks again!

Well, I finally got back into these radios.

Subbed the speakers and got the same sound quality. :thumbsdn:

Replaced 3 electrolytic capacitors in each and the sound level improved!:banana:

https://farm2.staticflickr.com/1582/...b7d1d7c3_z.jpg

https://farm2.staticflickr.com/1538/...b93833d7_z.jpg

I wonder it they had class AB output that slipped into class B (B has too much distortion for audio).

I think it's more a matter that my memory of what it sounded like in 1970 wasn't very good. After the way I treated stuff when I was a teenager this radio has no reason to still be in its original assembly.

Here is the schematic from the inside cover. The three capacitors I replaced are marked in red:
https://farm2.staticflickr.com/1479/...102f12ac_z.jpg

Love those early transistor radios ! - You should check all the resistors in the circuits
from the volume control and all to the right of it.... Maybe 3 - Ha Ha ! The single
resistor providing less than stable biasing may lead to poor quality sound by leaving
the transistor not quite turned on, and giving you what may actually be a clipping kinda
sound because it's not turned on until biasing level sound arrives at the transistor...
Poor quality speech is kind of a clue there..... Transistor turns on and off
giving a choppy voice, not a varying level amplification if it were biased on
all the time.....

R11 R13 R14 R15 R16 ?? Too Small to see clearly right now.... Amp supply & biasing.
If they check out, then I guess you'll have to check the transistors....
Could have something open.....

It would be interesting to follow a sine wave through the circuit to see what is going on....

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