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Mesa 400...6550/KT88?

Chef

Chef

In Memoriam
May 23, 2004
41,814
18,945
65
Columbia MO
Disclosures
Staff Reviewer; Bass Gear Magazine
#1
I recently bought a Mesa 400.
It came to me with new JJ 6L6's in it, one of which immediately vibrated apart: guts flying around inside the tube, fuses blown; lots of drama!

Looks like I'll need to re-tube the whole works again, so...this amp is supposed to have 6550's in it, right?
Which are same as KT88's, right?

Anyone running with these; even better yet if you ran 6L6's previously and can report on the difference.

thx-alan
 
#4
My 400 came with EH 6L6s. I got these results with my amp, my tubes, my bass, and my ears, yours may vary. To quote my old post:

Got around to trying the 400 with different power tubes, drawn from my stash. I left the volume and all other knobs where they had been from the last time I played.

Electro Harmonix 6L6 (it had these when I bought it): Earliest breakup, thicker sound, punchy.

JJ6L6: Cleaner, but a bit thin and sterile sounding compared to the others.

Mesa 6L6 STR 420: About as clean as the JJ, but "meatier" sounding.

JJKT88: Totally clean, perhaps a bit louder than the 6L6s. Sounds the most like the 400+ with these, but still seems overall a bit brighter.

Conclusion: The KT88s were nice, but since the 400 is sitting on a 400+ it's rather pointless. I put the EH tubes back in it.


Since then I've sold the 400 - it seemed to me my D180 could get very close to the 400 for clean tone and volume, plus having a few tricks of its own, so the 400 was redundant.
 
#5
I've been using JJ KT88's in mine. When I talked to Bob from Eurotubes about buying a set of 6550's, the KT88's is what bob handed to me.
Alot louder with a little deeper lows and low mids. I actually had to turn the volume knob down a notch from where it was using 6L6's. Yes just like Fealach said, it's just like the 400+.

I picked up another 400 a couple weeks ago, but I think I'll leave it with 6L6's for that easier to break up-dirtier sound.
 
#6
I've used JJ KT88's in my 400 and it sounds great!!! As far as I know you'll end up with more overall power using 6550/KT88's vs. 6l6's in that amp. I might be wrong, but let me put it this way, I'm completely, and I mean completely satisfied with my JJ KT88's in my 400. I also use ECC83s's for my preamp tubes.
 
#10
i much prefer 6550's to 6L6's for just about everything. cleaner and bigger sounding all the way around and i even like the way they overdrive better. i find 6L6's to have flubby low mids. EL34's and 6550's have the same pin-out but 6L6's are different so you will have to move a wire or two on each socket. it may have been just the heaters but i can't remember off the top of my head. fwiw, i've always had good luck with Winged C 6550's.

JR
 
#11
throbgod13 said:
.. but, they will be expensive..
Click to expand...

You think?


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I have never seen a matched sextet. Might be tough to assemble one since they're mostly found in pairs or singles from different sellers all over the world.

Besides, you don't want to do that.

Save the few remaining GE 6550A tubes for the poor 400PS owners who really need them. :D
 
#12
It was my understanding that the 400 was built to run 6550's and 6L6's are the aberration.
I'll call Mesa tomorrow, but still interested in more user reports...
 
#13
Fealach said:
You think?


[Invalid or Expired Link Removed]

I have never seen a matched sextet. Might be tough to assemble one since they're mostly found in pairs or singles from different sellers all over the world.

Besides, you don't want to do that.

Save the few remaining GE 6550A tubes for the poor 400PS owners who really need them. :D
Click to expand...

I'm glad I picked up a set a few years ago- they were still available then from KCA and Watford Valves, for example. Not cheap at the time, but I'm glad I did it, beautiful growl and breakup.
 
#14
From the Mesa 400 manual-which I forgot I had!:

"The 400 uses STR418 type 6550 power tubes. These are extremely rugged, powerful, high performance units available only from us.
Do not replace these tubes with the larger metal base type 665 such as Groove Tubes sell. First, they will not properly fit into the hold down clamps; second, they are considerably more expensive; third and most important, they will fail constantly in normal use and will invalidate your warranty.''

So, is Mesa really the only place to source these?

thx-alan
 
#15
One Drop said:
I'm glad I picked up a set a few years ago- they were still available then from KCA and Watford Valves, for example. Not cheap at the time, but I'm glad I did it, beautiful growl and breakup.
Click to expand...

I have a matched pair in my Twin Valve Combo, and I picked up a matched quartet (NOS) a while back, but I am waiting for the 'right amp' to grace with these beauties. :cool:
 
#18
Chef said:
From the Mesa 400 manual-which I forgot I had!:

"The 400 uses STR418 type 6550 power tubes. These are extremely rugged, powerful, high performance units available only from us.
Do not replace these tubes with the larger metal base type 665 such as Groove Tubes sell. First, they will not properly fit into the hold down clamps; second, they are considerably more expensive; third and most important, they will fail constantly in normal use and will invalidate your warranty.''

So, is Mesa really the only place to source these?

thx-alan
Click to expand...

Back when the the 400 was being made, Mesa used Philips 6550A's, which have a smaller diameter bottle than the Chinese "Coke Bottle" 6550's that Groove Tubes was selling at the time. Their base size is the same, so chalk one up to Mesa not paying attention on that. Their envelope shape does prevent Fender-style beartrap tube retainers, which Mesa used, from grasping them properly. Most importantly, Chinese 6550s of that era are unmitigated junk. Quality control was so lax, it was not uncommon to find cigarette butts inside them!

Nowadays, most any 6550 or KT88 will work fine aside from the tube retainers; most KT88's will still be too wide. I would caution one thing with KT88's. On old "to spec" KT88's, the heater current draw is slightly higher than a 6550's and if the Mesa's power transformer's filament winding is not de-rated, then extended use of KT88's could lead to PT failure which would require either a VERY expensive replacement or rewind. This, however, is less of a problem with modern KT88's since most just use the same heater as a 6550.
 
#19
Chef said:
From the Mesa 400 manual-which I forgot I had!:

"The 400 uses STR418 type 6550 power tubes. These are extremely rugged, powerful, high performance units available only from us.''

So, is Mesa really the only place to source these?

thx-alan
Click to expand...

Actually, Mesa hasn't had those tubes available in a long, long time. I use the EH 6L6's and am quite happy with them.
 
#20
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..
 

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