Mesa 400+ tube upgrade

CDweller · #1 12-30-2010, 06:37 PM

Can anyone comment authoritatively on upgrading the preamp and power tubes of a 400+?

I am contemplating changing the driver to a NOS Mullard CV4003- a milspec equivalent of a 12au7.

I also have a bead on 3 close tolerance NOS Siemens' E83CC's, a European 12ax7 equivalent.

The plan is to change out the preamp tubes first, substituting the Mullard for one of the 12ax7's, and the other 3 with the Siemens E83CC's.

Does using the really good NOS tubes really make a significant difference?

Also contemplating the adjustable bias mod in preparation for some NOS GE 6L6GC's, but that might not be really necessary if the amp's tone improves enough with just the preamp tube swaps.

The Mesa is a lightweight tube amp, comparatively speaking, but it's got to earn its keep tonewise. It's going head to head against my Reeves 225, and one will have to probably go at some point. Thus I'm trying to maximize the Mesa's potential. I am looking to get rid of any sort of grind factor (sacrilege, maybe..) with the Mesa, and thus the 12au7. Just looking for clean, authentic tube ampification with little coloration-eq can do that work, and any grind or grit can be done with outboard effects.

LiquidMidnight · #2 12-30-2010, 09:27 PM

I can't comment on the NOS Mullards, but I put a set of newly manufactured Mullards in the preamp of my 400+. They weren't bad, but I thought they were kind of harsh in the high end and were a little lacking in headroom. However, you YMMV with NOS. I ended up putting a set of Sovteks in and I'm very happy.

Classickbass · #3 12-30-2010, 09:37 PM

The most tonal difference you will experience is by replacing the V4 preamp tube, the one to the far left when looking at it from the front, with a 12AU7. It will clean up the gain and give you more headroom. You can swap out preamp tubes by yourself and with relative ease so the best bet for testing different tubes is to try them. There are some who swear by NOS tubes and others who think new tubes are better, it is all personal preference. I had my tech go through my 400+ last month and install all new JJ tubes, filter caps, and do a dual pot bias mod. It sounds a LOT better now. Of course, I had a blown tube when I took it in.

Edit: The preamp tubes don't need to be matched as they are self biasing. It certainly won't hurt but it is not needed.

jimbilly · #4 12-31-2010, 12:51 AM

I also had the bias pot mod (cermet?) done to the 400+ I used to own, - that's money well spent.
I think you will have a really hard time finding a bias matched set of vintage 6L6GCs for that amp, you'd pretty much have to set yourself up to buy a whole bunch of them and sort out a matched set. I'm kind of a tube snob, -I've got blackplate RCAs in my best amp (+ some spare pairs), and nice vintage tubes in the other good vintage amps, but I didn't attempt to put together a set for the 400+, I'm sure it's possible, but it would be tough, and really expensive.
Some of the newer 6L6GCs sound really good (like Sovteks, including their 5881s), even some of the newer Chinese 6L6GCs sound really good.

CDweller · #5 12-31-2010, 02:02 AM

Quote:

Originally Posted by jimbilly

I also had the bias pot mod (cermet?) done to the 400+ I used to own, - that's money well spent.
I think you will have a really hard time finding a bias matched set of vintage 6L6GCs for that amp, you'd pretty much have to set yourself up to buy a whole bunch of them and sort out a matched set. I'm kind of a tube snob, -I've got blackplate RCAs in my best amp (+ some spare pairs), and nice vintage tubes in the other good vintage amps, but I didn't attempt to put together a set for the 400+, I'm sure it's possible, but it would be tough, and really expensive.
Some of the newer 6L6GCs sound really good (like Sovteks, including their 5881s), even some of the newer Chinese 6L6GCs sound really good.

That's a fact. It can be done, but you're looking at about $1200 for 12 matched NOS GE 6L6GC's, which doesn't really make too much sense with this amp...unless it sounds unreal if done. I'm not sure exactly how good the 400+ can get, and it seems to be geared for the more rock oriented/grindy sort of players. Regardless, the plan is to install the good stuff in the preamp, including a 12au7 (an nos Mullard CV4003 has come my way) in the driver slot and see how that sounds. At that point, it seems like the next step is the adjustable bias mod, and it might be time to call it a day.