It's nice not having to break out a multimeter to play music.
It's my view that many audiophiles worry too much about the bias. With NEW tubes adjust initially, do 24 hour burn in, adjust.
Check again - not necessarily adjust - @ 50, 100, 200, 500, 1000, 2000 hours.
NOS are a whole 'nother kettle of fish as they sometimes take 24 or more hours to degas and many re-gas if not played quite frequently.
Input tube rolling REQUIRES level and channel balance adjustment to match what came out.
If one checks the cathode resistors, they may be 5% inductive parts with 300PPM TempCo.
I use precision wire wound non-inductive 1% 50PPM TempCo.
Line voltage variations and transformer temperatures may affect both bias and the output level, so do any rolling on fully warmed gear.
A small change in line voltage may affect B+ which affects bias, doubly so if the bias supply is unregulated.
I keep a cheep & cheerful digital voltmeter plugged into the system circuit.
If the voltage is off a little and the bias is off a little, all is well - provided all in the same direction.
The bias meters in my amps [avatar] are accurate to ±2.5mV - verified!
As long as they all track equally,
fuhgedaboudit.
If your bias check system has a switch, exercise it a couple of times before checking as the part likely has built up a little contamination.
Today's precision meters are both a blessing -accuracy- and a curse -precision.
A curse because they encourage knob-dicking.
Single turn cermet pots have a relatively short adjustment count, around 100-200 cycles.
Some lower grade parts suffer early mortality which can be fatal if open.
Do yourself a favor and replace single turn bias pots with multi-turn. Precision and life are both increased. Bournes 3339 series.
