Hi Bill, thanks SO much for that tip. I'm going to get that done ASAP. I have a whole stash of caps like that. Should do the trick. <div>73, Sandy AC1Y<span></span><br><br>On Tuesday, May 14, 2013, William Houghton wrote:<br>
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<div>Sandy,</div>
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<div>I had the exact same problem with my first SB-104A. No problem tuning up, a whistle blow would drive it to full power, but for normal speech I had to turn the mic gain up to the point where the audio amp broke into oscillation. After struggling with it for a long time I decide to connect an audio generator to the mic input. What I found was that it took a much larger signal to drive it at 300Hz than it did at 1000Hz. From about 1kHz and up the drive required was fairly constant. </div>
<div> </div>
<div>I solved this problem by replacing C204, 0.01uF cap, with a 0.1uF cap. I now make this change to every "B" board that comes across my bench.</div>
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<div>73,</div>
<div> </div>
<div>Bill<br></div>
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<b><span style="FONT-WEIGHT:bold">From:</span></b> Alexander N. Gerli <<a>ac1wye@gmail.com</a>><br><b><span style="FONT-WEIGHT:bold">To:</span></b> "<a>heath@puck.nether.net</a>" <<a>heath@puck.nether.net</a>>; <a>heathkit@mailman.qth.net</a><br>
<b><span style="FONT-WEIGHT:bold">Sent:</span></b> Mon, May 13, 2013 8:12:09 PM<br><b><span style="FONT-WEIGHT:bold">Subject:</span></b> [Heathkit] SB-104A low tx audio problem<br></font><br>Hi, gang!<br><br>Well, now that the rx is working a lot better, I have a new problem - LOW<br>
tx audio. I can get full power in tuneup, that's fine. With the mic level<br>set at 50%, I can get full-power with a whistle-up. But, nearly nothing<br>when speaking. I'm using a good Heathkit mobile mic I've had for years, the<br>
Turner 350 that was made for Heath.<br><br>Looking at the boards, I suspect something is amiss on Board B, the<br>Transmit Audio Board. Looking at the schematic, I'm wondering if the Q201,<br>the quad OP-AMP could be
the culprit? This provides the two stages of<br>amplification. LM3900N chips are pretty common and available. Before I head<br>to the 'Bay and get one (or maybe my local RS store might have one on a<br>blister-card), does anyone on the list have any similar experience like<br>
this, and what did you discover?<br><br>When I got this 104A three years ago, it ran great and has been a solid<br>rig. But, as with anything like this, past history is, well, just that.<br><br>Thanks tons for your kind help, folks!<br>
<br>73,<br><br>Sandy AC1Y<br>______________________________________________________________<br>Heathkit mailing list<br>Home: <a href="http://mailman.qth.net/mailman/listinfo/heathkit" target="_blank">http://mailman.qth.net/mailman/listinfo/heathkit</a><br>
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</div><br><br>-- <br><div dir="ltr"><div><div><div><div><div><div><font size="4">God Bless You,<br><br></font></div><font size="4"><font size="4">Alexander N. (Sandy) Gerli, Sr.<br></font></font></div><font size="4"><font size="4"><font size="4">54<font size="4">8 Allred Mill Road<br>
</font></font></font></font></div><font size="4"><font size="4"><font size="4"><font size="4"><font size="4">Mount A<font size="4">iry, NC 27030-2202<br><br></font></font></font></font></font></font></div><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4">Scotsmen <font size="4">walk about 900 miles each year.<br>
</font></font></font></font></font></font></font></font></font></div><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4">A Scotsman drinks around <font size="4">45 gallons of Whisky a year.<br>
</font></font></font></font></font></font></font></font></font></font></font></font></div><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4"><font size="4">Scotsmen get abo<font size="4">ut 2<font size="4">0</font> Miles Per Gallon.</font></font><br>
</font></font></font></font></font></font></font></font></font></font></font></font></div><br>