Mesa 400...6550/KT88?

[Fealach]

mesa customer service was kind of a let down on this one:
they say they shipped both ways, and "the amp is pre-biased for either" run whatever you want
the gent alluded to the reason they quit using 6550's was they could not get a reliable supply of them

So, fro mesa's point of view, they are interchangable in this amp..

That's pretty much what I got from them, only about the D-180. My 180 didn't like the JJKT88s, they lit up in a scary way and it sounded terrible. My 400 liked them though.

I can only dream about having a matched set of six GE6550A tubes for my Fender. I guess I'll never know how it sounds the tube that was, as the story goes, designed for the amp.

 

[Chriso21]

just get in contact with the dudes at eurotubes. They are great guys and can tell you everything you want to know about your amp and what tubes you need to get your amp sounding great - my mesa buster has sounded soooooo good since putting a full jj set up.

 

[timv]

I have a couple responses to this questions floating around here somewhere but I will explain what I have found and tested....

I've tried this experiment on an old 400, a d-180 and an old m-190 power amp. These 3 amps all show 6550's in the original catalogs but were eventually running 6L6's. I added adjustable bias to all 3 and tried a few sets of tubes and measured full clean power out. This is all based on measurements and electronics formulas, not sound, but gives you an idea of what I tested.

I ran a nice set of GE 6550's, which are now in my 400ps, a set of EH6550's, some jj 6L6's and a few others.

The GE's topped out the power output at about 180 watts before the first sign of distortion on my oscilloscope.

The JJ's were next at about 170 watts so the 6550's only put out about 10 more watts.

I did run a nice set of sylvania str 415 6L6's which were around the 160-170 watt range.

The other tubes were all around the 160-170 mark.

I think I ran some sovtek 5881's too and got around 150.

These are just test numbers. I think 6550's or KT88's would run a bit cleaner and probably have a little more low end than 6L6's.
I say try both types, might want adjustable bias to make sure you are getting the most out of the tubes, and listen to what your ears like the most.

Have fun......

 

[Chef]

Huh, that's really interesting.
I would have thought the 6550's would put out a lot more than 8% more than the 6L6's.

 

[Mika]

Huh, that's really interesting.
I would have thought the 6550's would put out a lot more than 8% more than the 6L6's.

There's only so much you can do with 510 V on the plates...
(based on measurement from my old Mesa M-180 power amp when properly biased for a sextet of Sovtek 6550WD's)

 

[timv]

Mika is exactly right.
These amps weren't made to pull the most out of the 6550's so they only were rated in literature at about 200 watts rms w/ 6550's, that is probably at 5% or so distortion, not sure what they spec at. I've bench tested some 400+'s at only 270 watts.
The SVT runs close to 700 on the plates to get up around 300 watts from 6. These boogies have about 520-540 on the plates (the ones I have tested at least).
Still, they are loud enough for any situation.

 

[jimmyjames77]

I have a couple responses to this questions floating around here somewhere but I will explain what I have found and tested....

I've tried this experiment on an old 400, a d-180 and an old m-190 power amp. These 3 amps all show 6550's in the original catalogs but were eventually running 6L6's. I added adjustable bias to all 3 and tried a few sets of tubes and measured full clean power out. This is all based on measurements and electronics formulas, not sound, but gives you an idea of what I tested.

I ran a nice set of GE 6550's, which are now in my 400ps, a set of EH6550's, some jj 6L6's and a few others.

The GE's topped out the power output at about 180 watts before the first sign of distortion on my oscilloscope.

The JJ's were next at about 170 watts so the 6550's only put out about 10 more watts.

I did run a nice set of sylvania str 415 6L6's which were around the 160-170 watt range.

The other tubes were all around the 160-170 mark.

I think I ran some sovtek 5881's too and got around 150.

These are just test numbers. I think 6550's or KT88's would run a bit cleaner and probably have a little more low end than 6L6's.
I say try both types, might want adjustable bias to make sure you are getting the most out of the tubes, and listen to what your ears like the most.

Have fun......

So I am currently running JJ 6L6's in my 400+ and feel that it lacks a little grunt on the low mids someimtes ( I'm running it with a Lakland 4-94 and a bergie 610 ) AND I feel that it distorts too easliy. Granted I do dometimes push it with the knobs out and turned up pretty good but still I think that it distorts too easily even for that. Not overly though...
In your opinion what set of tube to preamp tube combo would best get me that Clean headroom with the most mids and low end grunt? I need it thick and loud with plenty O' mids.

 

[Chef]

You can't run 6550's or KT88's in the 400+; only 6L6's.

 

[anderbass]

So I am currently running JJ 6L6's in my 400+ and feel that it lacks a little grunt on the low mids someimtes ( I'm running it with a Lakland 4-94 and a bergie 610 ) AND I feel that it distorts too easliy. Granted I do dometimes push it with the knobs out and turned up pretty good but still I think that it distorts too easily even for that. Not overly though...
In your opinion what set of tube to preamp tube combo would best get me that Clean headroom with the most mids and low end grunt? I need it thick and loud with plenty O' mids.

While my 400+ (w/full set of JJs/NV610/P-bass) seems to have plenty of clean headroom, mine seems to always
give me the urge to constantly twist knobs in a futile search for "stronger mids and lowend grunt" too. I don't know if
this is a common trait to the JJs, the amps design or the cab pairing, but I definitely don't have these issue's with my
SVT-II/NV610 pairing.

 

[Fealach]

Of course these terms are all subjective, and what you and I might mean by "mids and low end grunt" could be very different things; that said, IMO the particular 400+ I am most familiar with sounded fuller with Sovtek 6L6 or even 5881 power tubes than it did with the JJs. Finding the right power tubes to suit you can be an expensive experiment with the 400+.

 

[jimmyjames77]

Of course these terms are all subjective, and what you and I might mean by "mids and low end grunt" could be very different things; that said, IMO the particular 400+ I am most familiar with sounded fuller with Sovtek 6L6 or even 5881 power tubes than it did with the JJs. Finding the right power tubes to suit you can be an expensive experiment with the 400+.

I agree, terms are subjective.
So it might be that the JJ's are the problem???

Can you or can you not run 5881's in this head? What are the sonic differences between the 6L6s and the 5881s?

 

[Fealach]

My brother, who owned this head before me and now owns it again, ran Sovtek 5881s in it for several years, the shop he had it serviced at replaced the original tubes with them. I got a set of JJs when I got it from him, kept those tubes for my guitar heads when he got the head back, now it has Sovtek and Mesa 6L6GCs.

As far as I know the 5881 is a 6L6 "type" tube. I have heard claims the amp will have less power with these than with 6L6 tubes but haven't measured it and didn't notice a volume difference, or really much difference at all with the 5881 vs the Sovtek /Mesa 6L6 combination it has right now. My bro claimed it was smoother sounding with the 5881s when he had it retubed, but back then I didn't pay much attention. It seems to me with any functioning tube the Mesa tube heads will sound good, but some people may prefer the slight differences in various tube brands.

 

[jimmyjames77]

My brother, who owned this head before me and now owns it again, ran Sovtek 5881s in it for several years, the shop he had it serviced at replaced the original tubes with them. I got a set of JJs when I got it from him, kept those tubes for my guitar heads when he got the head back, now it has Sovtek and Mesa 6L6GCs.

As far as I know the 5881 is a 6L6 "type" tube. I have heard claims the amp will have less power with these than with 6L6 tubes but haven't measured it and didn't notice a volume difference, or really much difference at all with the 5881 vs the Sovtek /Mesa 6L6 combination it has right now. My bro claimed it was smoother sounding with the 5881s when he had it retubed, but back then I didn't pay much attention. It seems to me with any functioning tube the Mesa tube heads will sound good, but some people may prefer the slight differences in various tube brands.

Yeah I'm starting to think that with all these opinions back and forth that the difference you'd hear in a tube change is a nothing that can't be done with either a pre amp tweak or actually manipulating the knobs.
Thanks for the info,
Jim.

 

[BassmanPaul]

I have a couple responses to this questions floating around here somewhere but I will explain what I have found and tested....

I've tried this experiment on an old 400, a d-180 and an old m-190 power amp. These 3 amps all show 6550's in the original catalogs but were eventually running 6L6's. I added adjustable bias to all 3 and tried a few sets of tubes and measured full clean power out. This is all based on measurements and electronics formulas, not sound, but gives you an idea of what I tested.

I ran a nice set of GE 6550's, which are now in my 400ps, a set of EH6550's, some jj 6L6's and a few others.

The GE's topped out the power output at about 180 watts before the first sign of distortion on my oscilloscope.

The JJ's were next at about 170 watts so the 6550's only put out about 10 more watts.

I did run a nice set of sylvania str 415 6L6's which were around the 160-170 watt range.

The other tubes were all around the 160-170 mark.

I think I ran some sovtek 5881's too and got around 150.

These are just test numbers. I think 6550's or KT88's would run a bit cleaner and probably have a little more low end than 6L6's.
I say try both types, might want adjustable bias to make sure you are getting the most out of the tubes, and listen to what your ears like the most.

Have fun......

Thanks for posting this, I was beginning to think I was going nuts. I had always assumed the 400 was meaning a 400W amp. When I first read the posts I went and dragged out my schematic collection and looked it up. I was trying to figure out how Mesa expected to get 400W out of six 6L6's or even six 6550's for that matter with a bit over 500V on the plates. I estimated a max of about 200W. Thanks for confiming that.

Great informative post.

Paul

 

[Chef]

my service tech surprised me. I didn't know he was back in town.
He was running sound at the venue I played last night, and had my 400 with him.
He said that he replaced one of the JJ 6L6's with a new like spec'd tube...and replaced the tube filament grid caps.
(is that a real thing? that's what I remember anyway)
He said you don't really know which let go first, the tube or the filament cap.

Just so happens I had my mesa diesel 115's with me last night, and an old G&L L1000.

DA-mn...I like this head better than I remember liking my old 400+. I didn't have the mesa cabs then.
It was real nice.

 

[A9X]

get NOS GE-6550A tubes.. intense power and headroom.. but, they will be expensive..

A respected engineer over here tested the EH 6550 against GE6550, and the EH bested it. You won't get any more power out of an GE than any correctly functioning new tube of the same type.

 

[A9X]

Mika is exactly right.
These amps weren't made to pull the most out of the 6550's so they only were rated in literature at about 200 watts rms w/ 6550's, that is probably at 5% or so distortion, not sure what they spec at. I've bench tested some 400+'s at only 270 watts.
The SVT runs close to 700 on the plates to get up around 300 watts from 6. These boogies have about 520-540 on the plates (the ones I have tested at least).
Still, they are loud enough for any situation.

At around 500V Va, a pair of 6550/KT88 should have no trouble doing 90W.

The lack of power from the 6550's is likely due to transformer turns ratio. A pair of 6L6 with near 500V (which is overspec for the screens) needs about 50% more than 6550's at the same B+. So optimise for 6L6, too high for optimum power out of the 6550's.

 

[tombowlus]

DA-mn...I like this head better than I remember liking my old 400+. I didn't have the mesa cabs then.
It was real nice.

Glad to hear that it worked out for you! FWIW, I also prefer the 400 to the 400+, though it's not a huge difference.

Tom.

 

[Chef]

I don't remember the 400+ being "real tubey like an SVT," but at this point I'm inclined to say the 400 may be cleaner than the walkabout...at least when both are pushed.
If you run master high and input low, the walkabout is pretty clean, but it can get pretty tubey when you crank the input level past the master level.
Perhaps it's the all JJ tube compliment in the 400 (and the fact that it's reall dang loud without being pushed hard), but the 400 seems to hold together pretty well.

 

[morebass!]

I bought a new 400 in about 1986. It came with 6L6 power tubes. Mesa had just switched over from the 6550s. I don't think it was necessarily a smooth transition. After I had it a while I noticed that some of the tubes ran very hot and some were cool. I took it to two different techs, neither of whom could figure it out. I eventually sold it (at a large loss).