"ZeeTso" wrote in message
...
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 he
http://www.fredsamplifiers.com.au/do..._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