Hi!Mark

.... I have one Harris RF 550/Rf551 rx and preselector...and I have some problem with the RF550...the AFC don't work(lamps green...yelow are ok)...and in the first 15-20minutes I have one noise brum ...brrrrr...and distort audio signal in all modes CW...SSB and AM...if you kind help me...with some ideas and one copy of service manual...many thanks!...Ricardo