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Title: Can't Shut Up Audio Post by: Carl WA1KPD on September 26, 2008, 09:59:43 PM I have been restoring a Marconi CSR5A.
Love the radio..... Except like Edith (All in the Family)it will not SHUT UP all the way I turn the AF gain all the way down and I can still hear sigs I know that:
Next stop is C86 Any thoughts? Title: Re: Can't Shut Up Audio Post by: K1ZJH on September 26, 2008, 10:16:19 PM this might be a worth a shot, since I've seen it happen in antique radios...
Make sure that the volume control, R37, has resistance across the outside legs. If the ground connection is open to the carbon trace, you will never be able to control the audio gain. Could be a bad contact between the terminal and carbon track, or an open carbon track?? Pete Title: Re: Can't Shut Up Audio Post by: Carl WA1KPD on September 26, 2008, 10:29:05 PM Hi Pete
Good thought but even grounding the wiper ends up with some AF coming through.... But where is it coming from???? Title: Re: Can't Shut Up Audio Post by: w3jn on September 27, 2008, 08:10:36 AM Are all those shielded wires going to the vol control and tone control bundled together? Bet there's some capacitive coupling going on between them if so. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Other thing is the cathode of V6 isn't grounded directly. C89 is supposed to bypass all audio to ground at the cathode. If it's bad, there's gonna be audio there even tho the grid is shorted to ground because the diode section of V6 is the detector. Suggest you replace C89 and also bypass that cap with a .1 or .01 to get rid of any residual RF there as well. |