Need help Preamp went to starting mode .

My ARC SP-14 Preamp was acting strangely yesterday while I was playing second CD. Need your help to troubleshoot the cause.
The setup includes SP-14 with 2 Y connectors to Bryston 9B-ST for bi-amping Martin Logan Sequel II through active crossover (Vendetta Research).
It's been that way for last 2,3 months, then suddenly during playing 2nd CD, no sound came out and the LED on SP-14 got dim as if it's in warming up stage.
Turn off the amp and preamp, then turn on the preamp ony, it went through warming-up and "ready" as usual. The moment I turned on the amp, the LED on SP14 immediately got dim.
I repeated this for 2, 3 times and it happened exact same way.
I'm confused and not sure if it's the power source was weak (we're running the AC that time), or the tube (SP-14 is hybrid) went bad, or something else.
If you have any experience/guidance on this. please let me know.
The SP-14 has a circuit that detects wall voltage dips (and peaks too I think.) When/if that occurs, the preamp will switch back to "standby" mode and if you do nothing it will go back into "operate" mode after about 45 seconds. (It talks about this in the Owner's Manual.)

You could get a power regenerator/conditioner unit that maintains constant 120V, or put the preamp on its own circuit so it's not affected (as much) by other devices on the same dircuit turning on and off.
Thanks Nsgarch !
I got the SP-14 without manual, do you know where I can get a copy ?
Contact ARC at:

Audio Research Corporation
3900 Annapolis Lane North
Plymouth, Minnesota USA 55447-5447
Phone: 763-577-9700 Fax: 763-577-0323

(they don't have consumer email)

FIRST, ask to speak with a service technician (I recommend Chris Ossana) and discuss this function with him. THEN, ask if they can provide you with an Owner's Manual, or where you could get a copy. I don't have my SP-14 any more or I'd make you a copy. You might be able to get one through the folks at Audio Research Database: