Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Transistor Radio

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 05-18-2008, 07:19 PM
Blast's Avatar
Blast Blast is offline
blast, blast...
 
Join Date: Jun 2007
Location: Kansas City
Posts: 217
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.



Reply With Quote
  #2  
Old 05-18-2008, 09:37 PM
Celt's Avatar
Celt Celt is offline
Peanut Head
 
Join Date: Nov 2002
Location: Paragould, Arkansas
Posts: 1,746
I see three electrolytic caps that I'd consider replacing. Be sure to use the same values (voltage ratings can be higher).
Reply With Quote
  #3  
Old 05-19-2008, 10:14 AM
Reece's Avatar
Reece Reece is offline
VideoKarma Member
 
Join Date: Jul 2004
Location: Cleona, PA
Posts: 2,178
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
__________________
Reece

Perfection is hard to reach with a screwdriver.
Reply With Quote
  #4  
Old 05-24-2008, 02:19 PM
Blast's Avatar
Blast Blast is offline
blast, blast...
 
Join Date: Jun 2007
Location: Kansas City
Posts: 217
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!
Reply With Quote
  #5  
Old 02-07-2016, 06:53 PM
Blast's Avatar
Blast Blast is offline
blast, blast...
 
Join Date: Jun 2007
Location: Kansas City
Posts: 217
Well, I finally got back into these radios.

Subbed the speakers and got the same sound quality.

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




Last edited by Blast; 02-07-2016 at 07:12 PM.
Reply With Quote
Audiokarma
  #6  
Old 02-07-2016, 08:55 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 14,758
I wonder it they had class AB output that slipped into class B (B has too much distortion for audio).
__________________
Tom C.

Zenith: The quality stays in EVEN after the name falls off!
What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
Reply With Quote
  #7  
Old 02-07-2016, 09:07 PM
Blast's Avatar
Blast Blast is offline
blast, blast...
 
Join Date: Jun 2007
Location: Kansas City
Posts: 217
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:

Last edited by Blast; 02-07-2016 at 09:15 PM.
Reply With Quote
  #8  
Old 02-14-2016, 09:13 AM
Username1's Avatar
Username1 Username1 is offline
Not sure how I got here.
 
Join Date: Dec 2009
Location: Orange County NY
Posts: 3,584
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....

.
__________________
Yes you can call me "Squirrel boy"

Last edited by Username1; 02-14-2016 at 09:30 AM.
Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 09:23 AM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
©Copyright 2012 VideoKarma.org, All rights reserved.