ARC SP-6 Warmup time

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.

My backup SP-6B preamp takes about a minute to stop blinking. A call to ARC service will give you good information. ARC has a great service crew with quick turn
around. Keep in mind your preamp is over thirty years old. The 6B I bought in the mid eighties has been serviced 3 times by ARC...All the best..

I owned a couple different versions of this preamp. The 6B and later did have a "timer mute" circuit, but I remember it only took a minute or two at most to unmute. It was a long time ago,so maybe I've forgotten.

Here is an excerpt from a 6B owner's manual:

http://www.arcdb.ws/SP6/ARC_SP6B_flyer4.jpg

The SP-6C-1 was my favorite, followed by the 6E.

Nope, it's not normal. I would recommend calling Audio Research. It sounds like you will be sending it in for repair. I hope you didn't pay too much for it. This is why a 9/10 rating on these older units is not accurate. The faceplate may be free of scratches, however, the electronics is 30 years old and failing. Also, if you want your preamp restored to original and sound the way it's supposed do not send it to anyone except Audio Research. It may cost a little more, but it is well worth it.

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.