Tube lengths and some other questions.

I recently acquired a Nomad 100 combo from craigslist and included in the deal was a box full of "Semi-used but still good tubes" Well, I got bored the other day and just started glancing at all the different tubes, all of them are 6l6 Mesa's with the exception of a full set of Groove Tube 6L6's. When i started to lay some of them side by side, I noticed that some of the tubes were longer than others, and that some had an indention in the very tip of the glass whereas others do not (for instance the set currently in the amp all have indention's in the tips but none in the box did) Also, some of the tubes are STR 440's, some are 430's and some are 425's and the 425's look quite a bit different from the higher number variants.

I am a noobie to the tube amplifier world and was wondering what any of this means?

The only thing that matters are the STR numbers and the color codes (Distortion ratings for Groove Tubes). Find out which power tube sockets are paired and put the same STR model AND color in those two sockets. (A 100 amp should have 4 power tubes, resulting in two pairs of sockets.) STR 430 and 440s are different generation of 6L6GC, with 440 being the most recent. The STR425s are a slightly different animal known as a 5881. You must make sure these tubes are suitable for your amp. For instance, a Mark IV can accept 5881s, but only in the outer sockets with other tubes in the inner sockets OR if all four sockets use them. Mesa does not want people running 5881s in the inner sockets if different tubes are in in the outer sockets. Check your manual or call Mesa. If you don't have a manual, you can download one frm Mesa's website: http://www.mesaboogie.com/

Only run Groove Tubes with Distortion Ratings or 4. 5, or 6 in Mesa amps.

So, now onto a pre-amp tube question. The amp sounds a bit muddy and I cannot seem to get the bass leveled properly, so that leads me to believe the Pre-amp tubes are a bit old. In shopping around I noticed that Mesa sells standard AX7 tubes, but they also have SPAX7 tubes, after looking at their site they claim they are higher quality and provide more control over tone shaping and gain. I Was wondering if this was true or not?

The SPAX7 is considered to be more quiet and reliable than the standard 12AX7. For this reason, it's a good choice for V1, which has the most influence over overall tone.

A muddy sound could also indicate worn power tubes. Preamp tubes tend to be noisey (crackling, swooshing) or microphonic (feedback) when they need to be replaced. Tubes in V1 and the phase inverter/driver have the most global effect on tone. You could try replacing the tube in V1 with another tube (say V4) and see if it has any effect. This will tell you if V1 is the problem. The brand of tube can also make a considerable difference. Some tend to be darker (Mullards, JJs), while some are a bit brigher (Herleen, Holland tubes). Preamp tubes provide a very broad selection of tonal possibilities.

Maybe Nomads ARE muddy? I don't think so. You can just use the onboard e.q. if so. "Tone" is in the ear of the beholder.

Peruse this intersting thread:

http://forum.grailtone.com/viewtopic.php?f=4&t=36317

- Pat

shytfayse said:

Maybe Nomads ARE muddy? I don't think so. You can just use the onboard e.q. if so. "Tone" is in the ear of the beholder.

Peruse this intersting thread:

http://forum.grailtone.com/viewtopic.php?f=4&t=36317

- Pat

Click to expand...

Great link! I don't see where he's suggesting Nomads are muddy in general, only that he's concerned his tubes may be causing degradation or muddiness in his tone. My first Mesa was a Nomad 55, and I would not classify that amp as "muddy" either. The EQ recommendation is a good one; something my 55 didn't have.

I think it is the tubes because I can get some great tones out of the amp with the EQ scooping out the mids and boosting up the lows, but say if I am playing a riff involving a pedal tone on the bottom E string, everything gets run together and there is no clarity. That leads me to believe the pre-amp tubes are worn and causing some tone problems.

I also think I am losing some gain because I cant seem to find a consistent saturation point for each channel. I always have to adjust the amp before I start a practice session.

Oh and that is a great link, I am not thinking about opening up the amp and doing the high/mid cap removal mod.