OT: Tube Audio

lee davison leeedavison at yahoo.co.uk
Thu Oct 20 11:02:33 CDT 2005

> I didn't say nonexistant, only rare.  Dynaco was amoung the best
> then. The alternate was a filiment that was balanced to ground to
> minimize the amplitude of AC heater to cathode coupling, also only
> seen on quality gear.

Another, rarer, alternate used with directly heated cathodes is to
have two cathodes heated by a Scott wound transformer that gives
two phase AC current with a 90 degree phase difference. This
reduced heater generated noise because the noise is a function of
the square of the heater voltage and sin^2 + cos^2 = 1, effectively
a DC component.

I have only ever seen this arrangement used on broadcast equipment.



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