I have an interesting problem to present to the group. I'm in the process of restoring a later model R-4C that has a peculiar audio problem. The receiver is working fine with excellent sensitivity on all bands, except that on 80m when I turn on the crystal calibrator, I hear what appear to be weak, but very raspy spurious birdies in between the 25 KHz markers. When I vary the volume control, the birdies sweep through the passband of the receiver. Also, when listening to the audio output with a pair of headphones when the receiver is muted, I hear the usual low level hum that is typical for the R-4C, but it changes characteristics over a relatively small range around the 9 o'clock position of the volume control. The hum does not change in volume, it just sounds rather raspy over this small range, similar in characteristic to the birdies I hear in between the 25 KHz markers. Is it possible the audio output stage is self oscillating at some odd frequency and is somehow mixing with or modulating the output of the crystal calibrator?
I don't have access to a scope, but I do have access to a good quality Fluke DVM and an IFR service monitor. I would appreciate any suggestions on where to start looking. This particular receiver was in storage for about 15 years, so I wouldn't be surprised if there are some electrolytic capacitor issues. Thanks in advance. 73 de Bill, K9RZ _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
