OT: Tube Audio

[Allison]

>
>Subject: OT: Tube Audio
>   From: lee davison <leeedavison at yahoo.co.uk>
>   Date: Thu, 20 Oct 2005 17:02:33 +0100 (BST)
>     To: cctalk <cctalk at classiccmp.org>
>
>> 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.
>
>Lee.

The other technique is far simpler.  Balance, do the same thing only
in mirror image.  The reduction in hum and some types of noise is 
substantial and tube engineers understood it well.  The common
examples were 3A5s, 810s or maybe 813s in push pull pairs (both 
have directly heated cathodes). 


Allison