Bias increase after components burn in a few days??

[gbullimore]

hi all,
since completing my PLH mono's i have to say the sound is very good, it gives great insight into the recordings,
i'm tempted to day detail but i don't mean bright.

but one interesting quirk.
I set the bias to 1.95A total (after a long warm up)
this was happy and stable.
the bias would start at 1.6A and move up to full after warming up.

after several days of using a few hours each day, the bias had increased to 2.1A

I re-adjusted the bias to around 1.8-1.9A (after 5 hours warm up)
and this was stable,
the amps would take over an hour to move from bias at cold (1.6A) to full bias

but after a few days use the bias has drifted up to 2.0A,
now at power on it fairly quickly moves up to 1.9 then slowly increases to 2.0A.

the ambient temp now is about 10 deg colder than the first setup.

it's not a problem, but just wondered if anyone else had seen the bias increase after the components have a few tens of hours on them.

one thing this has taught me is how useful it it to have a bias meter on the amp. (well PSU so measuring actual total current draw per mono amp)
i only threw the meter in as i had them, but i will certainly add them in future when i build an F5.

 

[Nelson Pass]

Not really. I see bias increases, but I usually rack them before an hour has
gone by, so they continue to heat up for days, and then they get adjusted
again, usually twice.

Keep in mind that ambient temperature and ventilation (location) and
line voltage all play a big role in this.