From: info@turneraudio.com.au   
      
    Alex: Your digressions are always entertaining... Thanks. As for this DC or   
   AC heating of the tubes -- I do not care, since (IMO) the best tube is a   
   transistor anyway.    
      
   Its getting near Xmas, so lets not get christerical about what tube is best,   
   the one with va-koomy inside, or the other one mit de sandanshit inside.   
   Maybe one has too little of anyfink innit, and tuther has too much of somink   
   innit, and what might be best has yet to be invented, although mosfetishistas   
   have done a fair old job of faking it, so that you'd think there were about   
   100 KT88 within one    
   good power fet, with all of them forbidden to run at 30 Watts of Pda.   
      
   I am not a masochist to go into business of creating problems resulting from   
   using tubes in general and DHTs in particular, and then overcoming the   
   problems with bunches of 15000uF capacitors, heat dissipating resistors and   
   other stuff.   
      
   Ah, but ya got one thing wrong, I'm a sadist, inflicting fabulous hi-fi onto   
   infidels who hate vacuums. There's a gleam in my eye as I turn on the power,   
   and serve 'em up a dish of 15,000 uF sausages.     
      
    (However, you are lucky that audiphooles do exist, which gives you bread plus   
   enjoyment from fiddling with tube electronics.)    
      
   Weel, I guess I could say I'm lucky, but the pay rate for fixin up phules IS   
   LOW. But its only been possible because ppl have a listen to music via tubes   
   and they often have a little religious mystical experience which is a kind of   
   audiologladical    
   psychotic audiogasm. Suddenly, out of the blue comes this dreadful question,   
   "why did I spend so much on huge lumbering SS gear with 0.0000000000000000001%   
   thd at 1,000,000 Watts? I just can't help how ppl think, except to say, a   
   little while later, "now    
   that'll be $4,000 please". Christ, you see the crap they buy for $20,000.      
      
      
   The point I was making is purely of academic interest. Though this guy Steve   
   correctly discovered the phenomenon of doubling of the um frequency, he   
   misunderstood its cause attributing it to temperature modulation, while in   
   fact it is caused by "anode-   
   bend" full wave heater voltage rectification on both end of the filament.   
      
   Ah well, it should be common mode for a PP amps and thus not appear   
   differentially across the OPT. I guess with 2 tubes in parallel SE, maybe   
   having heater voltges in opposite phases, you get cancelation.    
      
   But all such dreampt up cancellations are not perfect, and usually there has   
   to ba a damn hum nulling pot somewhwere, so for me, putting Vdc on DH cathodes   
   is OK. Usually the Vdc is quite small compared to grid bias Vdc, so   
   differences between emissions    
   at each end of cathode becomes negligible. I believe the 15,000uF was right   
   when it told me, " jus' lemme smooth 'tings ova fo yo bro, and den de amps   
   begin ta bop."    
   Patrick Turner.   
      
        
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)