John: If you can hear the squeal, it is not ultrasonic. That would be rare I think.
Some tubes and their wiring have been known to oscillate at RF frequencies which may have several "carriers". The difference between these carriers may land in the audio frequency spectrum and be amplified by the modulator circuitry. Putting ferrite beads or parasitic chokes in the grids and plates of the tubes will not harm anything and may cure the problem. I have experienced this before. Loose nuts and bolts on the audio transformers or loose laminations are a more likely cause of accoustical feedback. Bad inter-stage bypass capacitors allowing electrical feedback between stages is the first place I would check. (B+ by-pass caps near the preamps/drivers). Good Luck. Charlie, K0NG ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/[email protected]/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: [email protected] To unsubscribe, send an email to [email protected] with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
