04-12-2013, 03:30 PM
Hello everyone,
I'm getting very close to victory on my 48-482! I have the FM aligned pretty well, and the AM and SW are about as sensitive as they can be (I spent a couple of hours monitoring late night AM radio to see how good the reception was--I was able to get all the full-power stations from around the country).
But I think the AVC is malfunctioning: the distant stations are very low on volume, though when I turn it up (3/4 to full), they sound fine without excessive noise, but when I roll across a local station, it just blasts me out of my chair. I'm sure the BC antenna is working fine, and the IF chain is continuous and zeroed in on 455 KC, but it seems like the AVC should be working better to attenuate the locals, and bring up the distant stations.
I tested R507 at 3.1 MOhms (should be 4.7 MOhms), but I'm having a real problem finding R506, the other branch of the AVC voltage divider. It's supposed to be on the pushbutton board, right next to C511, the coupling cap for the AM band. It isn't there. I've measured every terminal on that board, but I'm not able to find R506, another 4.7 meg resistor to ground.
Has anyone else had this trouble? How critical is the actual resistance of the AVC voltage divider? Would a bad reading like this cause the lack of apparent AVC on my AM band?
Thanks in advance to you all!
Mike
I'm getting very close to victory on my 48-482! I have the FM aligned pretty well, and the AM and SW are about as sensitive as they can be (I spent a couple of hours monitoring late night AM radio to see how good the reception was--I was able to get all the full-power stations from around the country).
But I think the AVC is malfunctioning: the distant stations are very low on volume, though when I turn it up (3/4 to full), they sound fine without excessive noise, but when I roll across a local station, it just blasts me out of my chair. I'm sure the BC antenna is working fine, and the IF chain is continuous and zeroed in on 455 KC, but it seems like the AVC should be working better to attenuate the locals, and bring up the distant stations.
I tested R507 at 3.1 MOhms (should be 4.7 MOhms), but I'm having a real problem finding R506, the other branch of the AVC voltage divider. It's supposed to be on the pushbutton board, right next to C511, the coupling cap for the AM band. It isn't there. I've measured every terminal on that board, but I'm not able to find R506, another 4.7 meg resistor to ground.
Has anyone else had this trouble? How critical is the actual resistance of the AVC voltage divider? Would a bad reading like this cause the lack of apparent AVC on my AM band?
Thanks in advance to you all!
Mike
