battery heated cathodes in vacuum tube amplifiers

dr barney -- Fri, 01/01/2010 - 10:26

     Because the cathode is a sensitive part of a tube amplification stage and the power that supplies it is difficult to make noise free, it seems to make sense to use batteries to supply the cathode heating current (with, of course, a shunting capacitor to get rid or noise picked up by the wires from the battery to the cathode heater terminals on the tube socket). It circumvents the need for worry about a.c. , power conditioners, cords, etc as far as the filiment heater is concerned, thereupon limiting matters to the plate voltage supply.
     I do not claim to have the cosmopolitan refinement of a professional audio reviewer, but when I switched from a.c. and even rectified filtered d.c. for the cathodes in my SET and drivers, it cleaned up noise I could hear and it made music sound more like it does in the concert halls where I go, even when I sit in a good seat.
     Has anyone else had any experience with battery heated cathodes?

dr barney -- Fri, 01/01/2010 - 10:30

Vacuum tubes began with battery heated cathodes. This should circumvent all the noise problems of a.c. or even rectified filtered d.c. cathode heater voltage. Has anyone else tried this?

Carlos Souza -- Fri, 01/01/2010 - 15:13

 I suggest that you do a Googlesearch. You will find lots of posts regarding battery heaters in places where people like to post about DIY audio.

Boomzilla -- Sat, 01/02/2010 - 21:25

 I can maybe see using battery current to heat the tubes for a phono pre-preamp where the signal is so low in amplitude that ANY AC on the heater would translate to noise.  On the other hand, the famous Dynaco Stereo 70 actually used AC to heat the output tubes' filaments!  By putting a diode & capacitor on the heater circuit, one could cut the bias down to about 20% of what was required to cancel out the hum previously.  For power amp tubes, I don't think that battery current is worth the trouble.  On preamps or phono preamps, yes.  Of course, I'm sure that LOTS of folks disagree with me, but the above is just my humble opinion.

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