Anyone interested in seeing an AM/FM radio restoration?

Discussion in 'Sparky's corner' started by DK71Buick, Aug 21, 2009.

  1. DK71Buick

    DK71Buick Wednesday Wrencher

    I almost forgot:

    One of the reasons why I want to restore the radio, is that I want to hear what one of these Delco FM models actually sound like when properly working, aligned and with known good and modern speakers.

    You frequently hear people talk about these radios sounding either muffled or 'warm', or some such. From looking at the schematic and thinking about my experience with other FM receivers of a similar age, then I find this hard to understand. I suspect any 'old' sound is more likely to be due to a combination of aged components, poor alignment and soft OEM paper speaker cones.

    Note that the maximum, theoretical power output from a model such as mine is only about 5 watts. In practice you should probably not expect more than 2 or 2.5 W before distortion becomes objectionable. So you may want to look for high efficiency speakers if you wish to make it LOUD. :grin:

    Most 'cheap' car radio speakers have a very low efficiency when converting electric power to sound. You can gain quite a lot in apparent volume from an original radio/stereo by buying high efficiency full range hi-fi speakers, though those are rarely cheap ($100-200 each). Nor are they likely to fit in the OEM panel cutouts.
     
  2. 12lives

    12lives Control the controllable, let the rest go

  3. 12lives

    12lives Control the controllable, let the rest go

  4. DK71Buick

    DK71Buick Wednesday Wrencher

    Yep, looks very nice.

    My text above was mostly concerned about using the original speakers from a classic car, which may yield less than perfect results. I haven't had a chance to listen to the reproductions linked above.

    Robert has an important point here. My suspicion is that some people may compare the audio from their original radio with what they can hear in their modern vehicle. Perhaps they do not realize that the old, very simple speakers in their classic car may be at least partly to blame for any difference they hear. Note that it doesn't help even if you manage to find some genuine NOS GM speakers, save those for the concourse restoration. It is the lacking mechanical design combined with 30 year old mushy paper cones, which ruins our day.

    I have a fair few original speakers sitting in radios from the fifties and up into the seventies, and - quite honestly - they are universally awful when compared to a modern, high quality full range speaker (system).

    Which is partly why I wish to test this, so you don't have to. :Brow:
     
  5. Itsa70

    Itsa70 New Member

    What happened to this offer of sharing alignment procedures?

    I am learning about these radios by attempting to resurrect a dead 71 AM/FM Stereo. It's a Pontiac (intruder alert) so I'm not sure a Buick is identical, but guessing Delco highly leveraged the same circuits.

    After a few mis-steps and bad assumptions I now have it making noise from both channels on my bench, thanks to help from a nice person named Matt on the Antique Radios forum
    http://www.antiqueradios.com/forums/viewtopic.php?f=6&t=315997 and the lucky find of a used DM-28 audio amp module from Turnswitch http://www.turnswitch.com/. Both amps are working, I can tune AM and FM.

    I was excited to find this thread, joined hoping to get suggestions on alignment, as my multiplexer does not seem to be working right. My red dot indicator light is on all the time, and the sensitivity adjustment for it acts like a front/rear fader but does not affect the light.

    Is DK71Buick or anyone else willing to guide me on alignment?
     

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