ARC SP-6 Warmup time

I enjoyed my SP-6b for 14 years. The power light stopped blinking after about 3 minutes. I normally let it warm up for an hour before listening. I suggest checking the bias voltage of V2 and V5 (The two middle tubes in each series of three). Unless your preamp has been modified, the bias voltage must be adjusted manually. If it is too far off, the unit will go into automatic mute mode (blinking light)at times.
If you are not handy with an electronics screwdriver and a voltmeter, have someone do it for you. It has been a few years, but as I recall, I set V2 at 155 Volts and V5 at 150 Volts. There are adjustment potentiometers next to each of those tubes. Check voltage from the capactitor next to each of those tubes to ground. It is shown in the schematics. Be careful. Don't go poking around in there too much. Voltages are very high. One time I put my voltmeter lead on a transistor case and measureed 550 Volts! I still have an old analog voltmeter that I used for calibrating bias voltage. A digital DMM should be fine as well. Just that I prefer analog :)

One other thing... The tubes could be worn, which would also cause the bias voltage to be off. Try some new tubes- especially if you do not want to poke around in there with a voltmeter. I recommend trying some NOS tubes. Search the web for some ideas and places to buy and which brand/vintage to get. I bought some on the bay for a very reasonable price and was blown away at how good they sound.

Just try some new tubes before doing anything else. High quality vintage gear is good stuff and can have many more years of service. The things to watch out for are corrosion and dried out electrolytic capacitors. I think it can be particularly rewarding updating vintage gear with modern high quality components. I bought my ARC SP-6b preamp in 1989. A few months later I had it modified by a buddy who was skilled in audio, a hobbyist and in the business of upgrading gear. Circuits weren't changed, just upgraded internal wiring with Litz, gold plated RCA jacks with teflon dielectrics, Wonder Caps and wire wound resistors in place of the carbon filled ones. My buddy also added better quality trim pots in the bias circuits. These were many of the things ARC incorporated into their later models. I used that preamp for the next 14 years. It sounded great. I only changed models eventually, because I wanted to get into the low output MC cartridges. I discovered NOS tubes too late in life. I'd love to go back and hear my old SP-6b again with NOS tubes.