[Boatanchors] Tube filaments

[Bill Cromwell]

Hi Ed...
     ...and Everybody,

In addition to the other valuable comments...

Using Well filtered, regulated D.C. on the heaters is not entirely
without value but direct conversion and regenerative receivers will
highlight that A.C. on the filaments/heaters is not the greatest source
of hum. In addition to using D.C. on the heaters we have to pay close
attention to grounding and shielding. Most of our homes (where we
operate most of the time) are saturated with 60 cycle A.C fields. If
anything introduces that energy in a differential mode you'll have hum
aplenty even in battery operated gear. It is possible to have no
noticeable hum on these radios even with A.C. on the heaters. Some of
the old time articles regarding regenerative receiver construction (or
direct conversion) to avoid hum pickup could have useful application in
almost any equipment.

Carl's comments about using regulated D.C. on the heaters in his
oscillators and low level stages point to some of the benefits of using
D.C. that way. That approach improves oscillator frequency stability in
measurable ways and according to his comments also helps in the other
low level stages. If we don't intentionally apply any 60 cycle (or 50
cycle) A.C. to any device in the radio we have certainly eliminated a
potential source of trouble. Moving the power supplies outside the radio
at the end of a power cable a few feet long also helps. If you are using
high impedance cans you'll want to do everything possible to eliminate
that hum.

73,

Bill  KU8H

73,

Bill  KU8H