please help preamp tubes not shining

Hi I purchased the Eclipse preamp new in 2011 and tonight after listening with pleasure as usual for half an hour the left chanel sound becomes softer and blur. So I turned it off and then waited for 2 minutes then turn on again.The sound becomes normal but I notice that the two tubes in front were not shining. so I switched the front 2 tubes with the back tubes. sound normal for both chanel but the front 2 tubes were not shining.Fuses are ok. red light both lit.sound ok. The problem is front 2 tubes not shining like they re not working at all but both chanel sound ok. Could anyonea help me indentify what is wrong with it?

Thanks in advance
Just got reply email from audio valve Germany with rude answer. Don't know what's wrong with them. But no more audiovalve product.
there may be nothing wrong with it. I've seen preamp tubes with almost no glow at all, and they don't get hot at all either. It sounds like it's working.
I agree with Sebrof. I have a tube phono stage that has (3) tubes. The middle tube, I have to turn off the lights and cup my hand around it to even see if it is glowing.

Sounds like your preamp is working fine. Just relax and listen to music...
hi thank you all for your help. I appreciated so much. I took the pre to the dealer and it is now fixed. the problem was from the small ic regulator. the pre sounds good but why the parts are so weak. may be I don't use it regualrly,just once every 2 weeks. would that be the cause?