01-07-2015, 12:37 AM
Hello, everyone!
I recently replaced all capacitors in a Philco 14B and my confidence as a relative newbie got a boost when, upon power up, the radio came to life. Both bands are active. Tonight, the broadcast band is wall-to-wall with stations, WWV is where it belongs at 2.5 MHz, and the Shadow Meter works!
Unfortunately, that power up and resulting reception of stations revealed a problem with the audio. If I advance the volume beyond a modest level (25% of the control’s range) the audio sounds distorted and raspy as though the speaker cone was torn. I pulled the speaker from the cabinet and found a cone with two minor tears on the outer edge, but the cone looks as though it got wet at some point and whatever solids were in that liquid reached the voice coil and dried out. The cabinet’s grill cloth was torn, and I presume someone dumped liquid on the speaker cone through the hole in the grill cloth. Photos can be found at the bottom of this web page:
http://k9uw.weebly.com/current-and-future-projects.html
At lower volume levels, the audio sounds fine. A typical listener would prefer more volume and would then experience the distortion.
What, if anything, can I do to deal with this problem? Is this “gunk” a potential source of the audio distortion reported above? If so, does anyone have a suggestion as to how to remove it? Is it reasonable to think that this stuff is contributing to the distortion? I have not replaced any resistors yet, so perhaps there are component-related issues that are impacting the audio quality?
Finally, I noticed that someone had wrapped a loop of heavy wire around the speaker’s magnet and audio output transformer, as if to hold things together. Things seemed solid enough so I poked around and found that the winding within the speaker’s magnet could be turned a bit if I pressed with my fingers. Could this be an issue?
Thank you, in advance, for any suggestions.
Mike, K9UW
Amherst, WI
I recently replaced all capacitors in a Philco 14B and my confidence as a relative newbie got a boost when, upon power up, the radio came to life. Both bands are active. Tonight, the broadcast band is wall-to-wall with stations, WWV is where it belongs at 2.5 MHz, and the Shadow Meter works!
Unfortunately, that power up and resulting reception of stations revealed a problem with the audio. If I advance the volume beyond a modest level (25% of the control’s range) the audio sounds distorted and raspy as though the speaker cone was torn. I pulled the speaker from the cabinet and found a cone with two minor tears on the outer edge, but the cone looks as though it got wet at some point and whatever solids were in that liquid reached the voice coil and dried out. The cabinet’s grill cloth was torn, and I presume someone dumped liquid on the speaker cone through the hole in the grill cloth. Photos can be found at the bottom of this web page:
http://k9uw.weebly.com/current-and-future-projects.html
At lower volume levels, the audio sounds fine. A typical listener would prefer more volume and would then experience the distortion.
What, if anything, can I do to deal with this problem? Is this “gunk” a potential source of the audio distortion reported above? If so, does anyone have a suggestion as to how to remove it? Is it reasonable to think that this stuff is contributing to the distortion? I have not replaced any resistors yet, so perhaps there are component-related issues that are impacting the audio quality?
Finally, I noticed that someone had wrapped a loop of heavy wire around the speaker’s magnet and audio output transformer, as if to hold things together. Things seemed solid enough so I poked around and found that the winding within the speaker’s magnet could be turned a bit if I pressed with my fingers. Could this be an issue?
Thank you, in advance, for any suggestions.
Mike, K9UW
Amherst, WI
Mike, K9UW
Amherst, WI
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