ARC SP-6 Warmup time

The mute time should not be more then 3.25 minutes. After that the LED should glow bright and the signal should be un-muted. If this is a B, or C version its usually caused by a leaky capacitor in the timer circuit and or a bad opto-coupler. If the unit hasn't been in for service, now would be a good time to do it. The B/C versions has multiple regulated supplies. A bad cap in any of them could cause a domino effect and take out the other regulators.

The '6B and later versions mute for one minute upon turnon.
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I own a modded 6-B which never took more than a minute or so. When I first glanced at the topic, I thought No the tone of my ARC 6-B was always on the colder, analytic side, and couldn't be warmed up by my usual tube rolls LOL!

Jeffrey, the circuit diagram says longer and can cause a thump if the mute releases early. The B and C preamp versions have a very long DC time constant and so it takes a while for it to stabilize. If your preamp is releasing after one minute, the cap in the timer circuit is the wrong value and releasing too early.

I've had the SP9, SP11 & SP14 and none of them ever needed more than 30-60 seconds to end mute mode. Agrre with others that you should call ARC and send it in.