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...