Hum elimination - can someone explain this - zobsky

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Hum elimination - can someone explain this

Browsing the web, I came across the following statement about hum elimination re. the 26 tube . Can someone explain if/how this works, and if so, why do A/C heaters on this tube still generate hum
Thanks
From http://www.jt30.com/jt30page/micKtubes/Why-5V-rectifier-vs-6.html

1. The early AC tubes (types '24 & '27, but not type '26) were 2.5 volt
heater types. The '26, with its 1.5 volt filament, was a special AC
design which attempted to eliminate hum by mutual cancellation of the
effects of the electric and magnetic fields from the filament. This
required that the choice of filament voltage and current be "just right"
in order to get the cancellation effect.

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Topic - Hum elimination - can someone explain this - zobsky 11:28:41 03/16/07 (2)

um, "This required that the choice of filament voltage and current be "just right" in order to get the cancellation eff" - Chris O 16:57:00 03/16/07 (1)

Re: um, "This required that the choice of filament voltage and current be "just right" in order to get the cancellation - zobsky 17:03:34 03/16/07 (0)

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