Hi guys, I thought I would relate a problem that my R-4B developed and what it took to repair it. The first symptom was some mild hum modulation transposed only upon strong CW signals. I thought that odd as it certainly didn't fit the typical power supply hum scenario. The receiver sat dormant for weeks and then used during the WPX CW contest this past weekend. The hum was worse and now classical AVC problems became evident. Backing off the RF Gain did not completely attenuate the signal. When switching to standby, the S-meter was not going fully up scale. Clearly, the AVC voltage was lacking and probably contaminated by hum. Sure enough the AVC neg power rail diode, D6, had failed generating only about -17V (normal is -80V)with a whopping 4Vpp of superimposed 60Hz. D6 had turned into a non-linear 1K resistor. Also R141 showed signs of mild toasting. It measured 3.3K vs 4.7K as marked. I suppose the extra AC current that had been fed to C91 (which I had upped to 22uF vs 8uF during a general recapping years ago) was a little too much for the half-watter. A IN4006 and a fresh resistor brought the rig right back to normal.
BTW, I did check the usual suspect tubes for grid emission while out of the case and found no issues. Dennis AE6C _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
