New mesa subway amps and cabs!

[agedhorse]

huh, I must have missed this detail with the original Walkabout ....
from the new WD-800 manual: "Tone shaping on the SUBWAY WD-800 includes an active Baxandall EQ"
does my Walkabout have a Bax EQ ? or is this just a new development for the WD-800 ?

I mean I do know that the Walkabout has an active Bass and Treble control with a passive Mid control (aside from the parametric EQ section).

also, after reading through the manual, I see that it reads "The preamp section includes a hybrid J-FET/12AT7 (or 12AU7) vacuum tube variable GAIN stage ..."
I've already read Andy's comments on the preamp tube choices, but am interested to know results a user could expect by using a 12AU7 instead of the 12AT7. I understand (more or less) that the differences in the various 12A-7 tubes is their gain factors, with the 12AX7 = 100, AT7 = 60 and the AU7 = 17, but what would this mean to my ears ? ... and what about using a 12AY7 ?

on edit:
I did some tube rolling with my Walkabout some years ago using some of the guidance from other more experienced tube rollers here and found that swapping tubes in V1 had little impact to my ears, but changes to the V2 tube had much more audible, and positive, impact. So, its with this in mind that I ask the question about the differences the various tubes might make.

The Walkabout also uses an almost identical Baxandall bass-treble eq arrangement.

Regarding tubes and "gain factor", in these circuits that's an almost insignificant specification compared to others that I had mentioned earlier. This is especially true for one section of V2, but V1 might also benefit some players from an AT7 due to where on the load line the circuit operates. This becomes a personal taste thing, and much of what was developed from the modeling and calculating these new circuits then listening to verify that the results were consistent with the math models.

 

[Lowendtech]

For my Canadian brethren, Long and McQuade head office in T.O. only has 6 WD’s on order at the moment. My deposit on one brings that # down to 5 as of yesterday.
Just an FYI.

 

[agedhorse]

Just to clarify, different tube parameters affect different elements in a circuit.

There are conditions where a 12AX7 can exhibit lower voltage gain than a 12AT7 if the plate curves and load line are not understood. These are the types of relationships that we deal with when designing circuits for a specific response and feel.

 

[pfschim]

Just to clarify, different tube parameters affect different elements in a circuit.

There are conditions where a 12AX7 can exhibit lower voltage gain than a 12AT7 if the plate curves and load line are not understood. These are the types of relationships that we deal with when designing circuits for a specific response and feel.

AH, after reading through so many of your detailed replies here, I have no doubt that there are plenty of other complexities in amp designs beyond just simple "gain factor" figures for how the preamp tube(s) behave in any given circuit. I'll never get to an experienced engineers, or experienced amp designers level of knowledge, but it is still interesting to try and reduce some of this complexity to useable ideas that can help players like me (and obviously others on TB) to better understand all of these interconnected elements and how the end up influencing how our amps operate and sound.

In the end, "if it sounds good, it is good" is still my fundamental guide, but I am always interested in expanding my knowledge/understanding.

 

[agedhorse]

The problem with trying to simplify all of the details into a single usable idea is that it leads to a false sense of security with incorrect understanding. It appears complicated because it is!

 

[Kirk Bryant]

I find the damping knob very interesting, I’ve never seen this on an amp before. Between that and the HPF, I think this new amp is rather unique. I do wonder though why, with the readily available new 1k watt modules, this newest generation of amps doesn’t step up the power level as well. But never fear, I’ll bet the next gen. latest, greatest, newest model will be the new WD1000 or Subway D1000 PLUS! Or will it be a 1200+??! haha.

 

[Chef]

I don't believe this is right.
It's been a long time since I talked to Bob Gallien about the Fusion preamp, but, I think you're wrong. I don't think it's tube one amplified by tube two, amplified by tube three.
Each of those 12ax7's has two gain stages, and I believe each of those 6, from three tubes, is used for it's own purpose here with the Fusion stuff; those purposes being input gain, and preamp eq functions.
I'm certain I'm mis-remembering exactly how they're used, but, it's something like:
1-input gain
2-treble eq
3-hi mid eq
4 low mid eq
5- bass eq
6- I FORGET ;--)

But!

Only a single pre amp tube?

The MBF-800 has 3.

The first tube is amplified by the second which is amplified by the third. Pushing the pre gives an amazing grit tone. And having 2 channels gives me both clean and dirt at the press of a foot switch.

 

[joel406]

I don't believe this is right.
It's been a long time since I talked to Bob Gallien about the Fusion preamp, but, I think you're wrong. I don't think it's tube one amplified by tube two, amplified by tube three.
Each of those 12ax7's has two gain stages, and I believe each of those 6, from three tubes, is used for it's own purpose here with the Fusion stuff; those purposes being input gain, and preamp eq functions.
I'm certain I'm mis-remembering exactly how they're used, but, it's something like:
1-input gain
2-treble eq
3-hi mid eq
4 low mid eq
5- bass eq
6- I FORGET ;--)

That’s how Jason at GK explained it to me when I had him on the phone. I called him after receiving my MBF-800 and inquired about the life of the tubes and where I should get replacement tubes when needed.

He was very forthcoming with information and that is a direct quote.

Tube one amplified by tube two amplified by tube three.

If that is wrong then you would figure Jason would know.

 

[MultiScaleMale]

That’s how Jason at GK explained it to me when I had him on the phone. I called him after receiving my MBF-800 and inquired about the life of the tubes and where I should get replacement tubes when needed.

He was very forthcoming with information and that is a direct quote.

Tube one amplified by tube two amplified by tube three.

If that is wrong then you would figure Jason would know.

MB Fusion 800 Specs — Gallien-Krueger

The quote: The signal path for gain, EQ, contour and the DI are 100% tube driven, achieving classic tube performance with 300V plates.

Plus, from the manual, you can see where the tube stages are used:

 

[BadExample]

I have no pig in this race, but

Tube one amplified by tube two amplified by tube three.

Amplified in what way? Amplified, I believe, is technically meaning increasing amplitude. It's also used by many, even good engineers, to describe other things. What was the context?

An Operational Amplifier - Op Amp, can be implemented have a gain of unity... or less.

 

[Fab Superlative]

on edit:
I did some tube rolling with my Walkabout some years ago using some of the guidance from other more experienced tube rollers here and found that swapping tubes in V1 had little impact to my ears, but changes to the V2 tube had much more audible, and positive, impact. So, its with this in mind that I ask the question about the differences the various tubes might make.

Maybe this will cue some responses from the beta testers that swapped & rolled for this particular amp?

FWIW as a general rule of thumb when I roll pre tubes, if a 12AT7 will work- that is what I go with. Why? because (to me) the 12AT7's seem to have a more 'musical' quality baked into them, when compared to the ubiquitous 12AX7's. And there are still plenty of primo NOS 12AT7's out there at way more attractive price points when compared to similar NOS 12AX7's and 7025's
As a side note, again from personal experience. The current crop of Mesa branded 12AT7's are right up there with most primo NOS 12AT7's.
It's nice to have a reliable current supply of new stock at bargain prices for a change.

Also (to me) the 12AT7's as a general rule of thumb again, have a lower noise floor when compared to 12AX7/7025's
High gain pre tubes are de riguer, for guitar amps, whereas in bass amps the overdriven hair of a high gain pre stage is not always desirable.
The musical tube compression/saturation that many players fall in love with, is actually produced by the sag of the power tubes anyway.
Perhaps this is where the 'damping' control and function of the new WD800 comes into play?

@agedhorse & crew, have been tasked with reproducing the legendary tonez of the OG Walkabout, with a lightweight/scaled up power section of a class D platform- no small feat by any measure. And with just what has been described here (since very few have yet to actually hear the new amp with their own ears) by just straight up and reading between the lines, it sure does look like they have met that lofty goal and have probably hit it out of the park as well. And I along with many others, can hardly wait to hear one of these for myself once they are released into the wild.

 

[Chef]

Aha!
Input gain A
aaaaaaand!
Input gain B!
That’s what I was missing.
My memory isn’t as bad as I thought




QUOTE="RichSnyder, post: 22047157, member: 33169"]MB Fusion 800 Specs — Gallien-Krueger

The quote: The signal path for gain, EQ, contour and the DI are 100% tube driven, achieving classic tube performance with 300V plates.

Plus, from the manual, you can see where the tube stages are used:

View attachment 3233540[/QUOTE]

 

[joel406]

I have no pig in this race, but



Amplified in what way? Amplified, I believe, is technically meaning increasing amplitude. It's also used by many, even good engineers, to describe other things. What was the context?

An Operational Amplifier - Op Amp, can be implemented have a gain of unity... or less.

I am not nor have I ever claimed to be an engineer. The quote from Jason stands on its own. If you want further clarification call him yourself.

 

[lowendrv]

I am not nor have I ever claimed to be an engineer. The quote from Jason stands on its own. If you want further clarification call him yourself.

I might be wrong . But every time I've had my GK's repaired it's been done at the factory . They have always got me to one the techs or Bob himself . Even when I've stopped in at the factory to pick them up .I believe Jason is a sales/support administrator . There might be some disconnect in there somewhere .

 

[BadExample]

Joel, I did not say your were acting as an engineer, nor did I mean to upset anyone. I just noted the explanation could mean something other than each stage amplifies another in terms of power, voltage, amplitude, etc.

I'd call, but like I said, no pig in the race here.

 

[Old Garage-Bander]

I find the damping knob very interesting, I’ve never seen this on an amp before. Between that and the HPF, I think this new amp is rather unique. I do wonder though why, with the readily available new 1k watt modules, this newest generation of amps doesn’t step up the power level as well. But never fear, I’ll bet the next gen. latest, greatest, newest model will be the new WD1000 or Subway D1000 PLUS! Or will it be a 1200+??! haha.

In my opinion, I think it’s getting to a point where you need to have something like a license for amps with that much power.

It’s like driving the big rig, 18 wheelers. Sure you can get behind the wheel, put it in gear and drive a block or two. But take it out on the highway without knowing how to handle that much truck, and there will be carnage. Big amps need big speakers (or lots of power handling capability in some form) otherwise there will be cab carnage. Those who get it will be fine, but without something like an amp CDL, things will get out of control. People will be blowing speakers left and right. The ability to throw more power at loudness has caught up to and will surpass the ability to provide speakers, in small packages that can handle that power.

If you’re playing venues that need to be that loud, your gonna get it from the sound guys.

 

[Chef]

“Need a license, too much power for the speakers etc.”

I used to regularly use a 3600 watt QSC power amp with speakers that were always less than that.

I now regularly use 800 watt amps with small cabs that are rated for half that.
So far this has never been a problem.
I just don’t dime everything in those circumstances.

 

[BadExample]

It’s like driving the big rig, 18 wheelers. Sure you can get behind the wheel, put it in gear and drive a block or two.

I like the analogy, but the average person couldn't drive a corn truck around the block, much less an OTR tractor, even without the trailer.

 

[detracti]

The way they describe that damping knob on the site makes me think it must be away to get closer to a traditional SVT type of a tone.

 

[Old Garage-Bander]

I like the analogy, but the average person couldn't drive a corn truck around the block, much less an OTR tractor, even without the trailer.

I know what you mean.
When I was in school I had a job washing and gassing the big rigs for a truck leasing company.
Every now and then I tried to back one in between two other trucks with about a foot of clearance on either side.
Bet you never saw a tractor/trailer jack-knifed in a parking lot?