Amp biasing question

@immatthewj

Depends on what your intentions are.

Are you planing on only checking the tube bias and then shutting the amp off and not listening to music, Then there is not any need to turn on the preamp.

If you want to check the bias and then listen to music then turn on the preamp and then turn on the power amp. Preamp not playing music. I leave my preamp on mute. Allow the manufacturer’s recommended time for the power amp to stabilize before checking the bias for each channel. My ARC amp says allow at least 15 minutes of uninterrupted stabilization time. I have have found to allow 30 minutes or so of uninterrupted stabilization time works best.

If you want to listen to music first, and then check the bias, first stop playing music then mute the preamp. Wait at least the recommended manufacture’s time for the amplifier to stabilize before checking the bias. In my case I allow the amp to stabilize for at least 30 minutes.

Also,... YMMV But but my two ARC amps are getting old. I have found I need to reset the bias on each channel, when I reset the bias on one channel and then reset the bias on the other channel. I usually have to fine tune the bias on the first channel again. I then recheck the bias on the second channel and sometimes I have to fine tune bias again on the second channel. Older ARC amps are a pita to bias the power tubes.

Also worth noting when it’s time to buy new power tubes buy pre burned in power tubes. It saves a lot of time checking the bias of new tubes without any hours on them at all... At least 48 to 72 hours pre burn in times on the tubes works well...

Also before installing new power tubes adjust the bias pots down a little first. Especially if the old tubes were biased regularly and were near their end of life... You can damage new power tubes if you don’t.

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My Audio Research amps are self biasing. 

@cleeds 

Ok. I guess that could happen. Fortunately never to me.
 

My ARC Ref amps have a 3.5 minute warm up before coming on-line and the preamp (Ref 6SE) has a 1.5 minute warm up before coming on-line. So unless I go get a cup of coffee between turning on the preamp and amp that will not happen. I guess ARC thought of everything. Cool.

Thanks, @jea48  , I just remember reading here that an ampifier should not be turned on unless it was hooked to a speaker load and had a preamp  connected to it and turned on.  And I am pretty sure I have read that an amp should be biased with the preamp turned off.  The two seemed to me to contradict one another so I was just wondering how folks were doing their biasing.

With all that above being typed, it is possible that I misunderstood something along the way.

Thanks again for the input. 

If an ARC amp does not have auto bias, then the amp should be on for 20 minutes before adjusting bias.

ARC amps can be on with no input cables, and without speakers cables connected. They are perfectly stable. This is not true for some other tube amps so it's best to check with them first. 

jea48's recommendations above are spot-on. Turn the bias pots down before putting in a new set of tubes!