From the SP6B owners manual. Page 6. Warm up timer mutes the SP6B outputs for 2 minutes after the power switch is turned "ON".
ARC SP-6 Warmup time
I just bought an Audio Research SP-6 preamp. It takes about ten minutes after powering on for the power lamp to stop blinking and the unit to start passing signals. Other than that it sounds perfect on all inputs. Is this at all normal? Does it indicate something is about to fail? Ten minutes to warm up is more than annoying.