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I have a marshall 2100slx with el-34 tubes and today when I was playing I looked inside the head and one of the power tubes were not glowing. Does that mean the tube has failed and needs to be replaced?

If I need to replace what would you guys say is a fair price to get my tube rebiased and retubed, this is after I buy some tubes for the tech to install. I plan to get them from here from : localhost/thetubestore.com/ne-el34.html . Should give any special comments on specific numbers I want from the tubes or should I just buy em in a quad pack thats already without caring about certain numbers I want?

My amp guys charges me $10.00 to set the bias, but I usually have the chassis out of the case, if not he charges $15.00
You could also have a phase inverter tube going out to lunch, if you have a known good 12ax7 or ecc83, stick it in the position nearest the power tubes, and see if your tube glows again. Just because you don't see a tube glow, doesn't always mean it is bad.If you had a really bad tube, you would get very little sound out of your amp, as it is a class a/b push pull design.

P.S. I don't know how the tube store rates their tubes, but you should call or email them, and tell them the sound you are after. Quick distortion, or a cleaner less distorted sound. Always have your Marshall re-biased,and replace the phase inverter tube at the same time.

I just started to get familar with tubes just a few weeks ago. Could you tell me what a phase inverter tube is? I just assume this just another name for a preamp tube, if I'm wrong correct me.

If it helps at all from the most right tube being 1 and the most left tube being 4, if you postition yourself in behind the amp. The 3rd tube is the tube that does not light up at all. If that gives you any more hints to the problem please tell me.

Thanks,
David

I don't know for sure what you mean, let me ask you- is this a 100 watter or a 50 watter?( do you have 2 or 4 EL34's?)
Without getting too deep into theory-
THe phase inverter is a small tube, although most people refer to it as one of the pre amp tubes, it is not involved with any tone stages, there should be a phase inverter tube for each power tube section. IN Marshall's it is always an Ecc83(English number for 12AX7) and is located nearest the power tubes.
It is sometimes refered to as a driver tube, as it 'drives' a set of output tubes.

P.S. if you want to learn a little about tube amps, and how they work, I suggest checking out this link- It's fairly easy to follow
from : localhost/www.guitaramplifierblueprinting.com/GTlink.html

My amp is the 100w version, but I currently have it on the low power mode so it becomes a 50w head. When it's on the 50w setting all the tubes are still on. It has 4 ECC83's and 4 EL-34's.

I'mnot real up on that model, but I suggest you take it in for a good checkup. couldn't hurt, and may save you lots of money in the long run. (Marshall Transformers are very expensive) Find out where the hot players in your area go to have their amp work done.