From: mynamespacedbydots@xs4all.nl   
      
   "ZeeTso"  wrote in message   
   news:ksam7f$rna$1@ls237.t-com.hr...   
   > hi there!   
   >   
   > first to state, i got no real expirience with vacuum tubes, but i   
   > understand basic electric/electronic principles, and have some soldering   
   > skills :)   
   >   
   > that said, i have a question regarding voltage and current for 12AU7   
   > (ECC82) heater in cheap and simple headphone amp. tube is in input stage,   
   > driving an op amp.   
   > now, design says that amp needs 12V DC power supply. there is an LM317   
   > current regulator in series with heaters, and it has 5ohm resistor giving   
   > max 250mA load (calculated value).   
   > with 12V DC supply voltage there is only ~10,5V between pins 4 and 5   
   > (heaters in series).   
   >   
   > what is confusing me is the fact that every 12AU7 datasheet says it needs   
   > 12,6V for heaters (in series).   
   >   
   > is this value absolutely necessary, or it might vary?   
   > how is that affecting tube performance and sound?   
   >   
   > i connected the amp to regulated power supply and noticed that it sounds   
   > better with higher than 12V supply voltage.   
   >   
   > to get 12,6V for heaters i need ~15V DC power supply, so i guess that   
   > would be best option.   
   >   
   > what says you?   
   >   
   > p.s. original schematic is in pdf file here:   
   >   
   > http://www.fredsamplifiers.com.au/documents/12AU7_Valve_KIT.pdf   
   >   
   > p.p.s. sorry for gramatics, english is not my native language...   
      
   In this configuration, and for 300mA heater current, the LM317 requires 3V   
   minimum input-to-output difference to work correctly .   
   Add that to the 12.6V heater voltage and get a minimum of 15.6V input   
   voltage.   
      
   Gio Re   
      
   --- SoupGate-Win32 v1.05   
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