[Hallicrafters] '101 hum

[RJB]

Andy

a couple more points re hum in boatanchors (these may have been covered in
the many response - if so, sorry if i am being repetitive)

Even if you have a correct impedance match to your headphones, you may still
hear hum for these reasons

1 - ground loops. These are basically witchcraft, but seem to be caused by
poor earthing of components in the audio section, for instance if the
headphone ground line is grounded at the front panel but not near the output
transformer/output tube. My R-390a's are terrible for this, and using modern
wide-range stereo phones sure lets me know.

2 - a bad transformer and choke layout on the chassis itself. The power
transformer is surrounded by a strong AC magnetic field which can be picked
up by the output transformer, if it is mounted too close. I have heard of
radios with hum in the headphones, even with NO output tubes installed - the
hum is being induced in the output transformer directly from the power
transformer. Hard to do much about that one without some rehasing of the
layout (verboten in boatanchor culture :(

73's

Bob Bennett, Maple Vly, WA