Greetings, I'd like to start a thread which discusses the AVC in the National RAO2 receiver. I've got one (built by Wells Gardner) that I'm about finished overhauling. It's very sensitive, dial calibration is perfect. A great receiver except for one little problem. The audio is affected by modulation peaks on the RF carrier. Yes, on an AM signal it should be to a certain extent, but received audio causes big changes in the AVC voltage. Looking at it on the scope I see up to 4 volts of change on the AVC line from audio peaks. I've checked all the AVC 500k resistors. Checked all the .01uf bypass capacitors, checked all the 6K7 tubes (and replaced a few weak ones), and the 6C8G AVC detector and 6F8G detector too. The .1uf bypass in the AVC rectifier circucit is also good. All these capacitors have been replaced, and checked for correct value. The AVC voltage drops quickly on audio peaks, and then you can see the discharge of the .1uf capacitor through the 500K resistor until the next audio peak. It's very annoying. S-meter bounces around too, as it should.
I've tried adding additional capacitance to the AVC line. As much as 2 uf. It helps but the AVC rectifier can discharge it much faster than the 500K resistor can charge it? Any RAO2 owners out there who have seen this in their receivers? Any suggestions as to a potential fault which is causing this? My intent is to get this going as an 80 meter AM station with a Harvey Wells Bandmaster transmitter, sure would like to use the old girl on the air....but that pumping audio is pretty objectionable.... Thanks, Wally Gibbons, AF7FH North Logan, Utah _______________________________________________ Boatanchors mailing list [email protected] https://puck.nether.net/mailman/listinfo/boatanchors
