> > >When I've had hum from the IF module, it in fact was caused by >heater-to-cathode leakage in the V507 limiter tube. > I've had that problem too. The fault doesn't show up on a tube tester! Cheers, Gord, VE3EOS -- Gordon L. Hayward, Ph.D., P.Eng., Associate Professor, Biological Engineering, School of Engineering, University of Guelph, Guelph, Ontario, N1G 2W1.