Just Got Home With A Mesa Nomad100 . . .

. . . and I have to say I am blown away to say the least. There is no "mud" goin' on on any channel. And CH3 is far from being "bright". Those are the words I kept reading about this amp on the web when I started looking into this amp. I picked this thing up for an amazing price from someone that needed to get rid of it for money to pay bills supposedly.

I did a quick checking up on things before I cranked it up here in my living room. The bias is a bit on the cold side at 26mA and 466V on the plates. It has a mix of two Mesa 6L6GC STR 430's on the outer sockets and two Mesa 6L6GC STR 420's on the middle/inner sockets - all biased within a few mA of each other. I have not taken the cover off of the five 12AX7's yet to see what's in there.

It just has a rip in the tolex on the top left joint as well as the joint is a bit separated. The kid said it had not been dropped or anything and I did not see any signs of that. He said that quite a bit of weight had been stacked on it. So I will have to fix that later.

But anyway, I was expecting to have to do some mods on this thing. But clarity on all channels and modes is awesome. And the reverb works great on all channels as well. So I will looki into it later to see if anyone did any work on it. The kid said it had no mods performed on it.

Only bummer is it does not have the 6 button footswitch, only the 5 button. So I will either have to find me a 6 button (anyone here have one for sale?) or mod it to take a separate one button footswitch for the EQ.

I am flat out stoked. This thing sounds better than the DC-10 I just got a few weeks ago.

Having a switchable eq seems hopeful at first, but in the end, I simply used my eq to compensate for the room and the speaker cab characteristics, and thus left it on, or never used it at all. The switchable feature may be more interesting for people who fluctuate between death metal and classic rock.

Out of curiousity, what type of music do you play the majority of the time, and what cab/speakers do you use?

Maybe the tubes are just really bad :lol: :lol: :lol: Or your ears have a high freq. roll off :lol: :lol: :lol: ...just kidding. Sounds like you got a good one. I love mine (a 55 watter) and the mods that I did just made it better at least to my ears. I didn't do them all BTW. Welcome to the red headed step child club.

Tommy_G said:

Having a switchable eq seems hopeful at first, but in the end, I simply used my eq to compensate for the room and the speaker cab characteristics, and thus left it on, or never used it at all. The switchable feature may be more interesting for people who fluctuate between death metal and classic rock.

Out of curiousity, what type of music do you play the majority of the time, and what cab/speakers do you use?

Click to expand...

I plan on trying this Nomad 100 as well as the DC-10 I just got as well, out in both the cover band and the new original project as well. The cover band plays the usual bar gig backyard party stuff, with a range of old 50's Rock through Beatles Hendrix Zep on up to some newer heavy Rock and Alternative. A pretty good mix of material.

The original project? Yeah, hard to explain that one. Think of Alice In Chains Incubus Foo Fighters LOL. Material is just being written as we go as I am trying not to rely on any of my older songs from many years ago.

I have many many cabs 4X12, 2X12 and even 1X12 and speaker configs. My favorite speakers are the old Celestion G12-65's. I also like the Hellatone 60L's. The main cab I haul around is my older Marshall 1936 2X12 with two G12-65's. I also have another 1936 cab with two early 90's made V30's that sounds awesome. I am thinking about running both these 2X12's together to mix the G12-65's and V30's.

I have been trying quite a few of my collection of amps in this new original project, as the amps are mostly many many different models of Marshall amps (am I allowed to say "Marshall" around here?). I have also been experimenting with slamming the front input of my old Fenders and my old Ampeg V4, with a few different Dirt pedals with interesting results.

But I do like all of the features on this Nomad 100. And the three channels should fee me up from using Dirt pedals. Though I still am going to experiment a bit with a few different boost pedals into the Nomad and the DC-10 as well.

earachemyeye said:

Maybe the tubes are just really bad :lol: :lol: :lol: Or your ears have a high freq. roll off :lol: :lol: :lol: ...just kidding. Sounds like you got a good one. I love mine (a 55 watter) and the mods that I did just made it better at least to my ears. I didn't do them all BTW. Welcome to the red headed step child club.

Click to expand...

I would say that all of the valves in this Nomad are actually old. The five 12AX7's all look to be original. And the seller did say that he thought the Mesa 6L6's needed to be replaced.

And I was the Red Headed Step Child growing up LOL. But it was a Long Haired Red Headed Step Child to be more precise.

:mrgreen:

Yep. A boost, an OD pedal or 2, an eq and a compressor will give you just about any sound you need. I put el34's in mine for a more Marshallesque sound.

Sounds like you have some great cabs, from the start of the modern era, and the speakers are probably broken in by now too . I bet the G12-65's would sound pretty great with Ch3, and the v30's pretty decent with Ch2, although greenies even better with Ch2, I would think. As far as pedals, if you have an OCD, put Ch2 on a pretty low gain crunch rhythm tone and hit the OCD....nice! Ch2 is taken from the Heartbreaker Ch2/High and I think the Heartbreaker Ch2 formed the basis of the Electrodyne concept as well, so excellent circuit and tone there.

If you are into the whole schematic analysing thing, you will be pleased to know that Ch2 is like a hot rod (cascaded gain) 1968 JTM 45/100 circuit, and Ch3 looks more like a modern Marshall, kind of a like a cross between a JCM800 and Mesa Rectifier if I recall correctly. Of course the preamp tubes themselves are biased a little differently than marshall does theirs, but the tone stack and coupling cap values compare pretty well.

I admit my major issue with the nomad is the low frequency cut in the NFB loop, but that can be somewhat compensated for by the graphic EQ.

One of these days I'm going to do a hail mary and throw in a pair of JJ 6v6's into the Nomad. Apparently they should be able to handle the plate voltages, but I'm not sure how the bias levels will work out.

Good info Tommy_G. Thanks for your input.

As far as trying a pair of 6V6's? I would only be brave enough to try the newer JJ 6V6S valves, as they are quite robust. I have tried them in a few of my JCM800 Marshall's with interesting results.

Which model Nomad do you have? When I tried the pair of JJ 6V6's in my '82 4010, I compensated for the different impedance of the 6V6's by setting my amp at half the cab load.

Does your Nomad have an adjustable bias? My Dual Caliber DC-10 was easy to turn into an adjustable bias. I just added a combination of a small 100K trim pot inseries with a 4.7K 1W resistor, then that goes across/in parallel with the main bias supply cap 220uF 63V. Gives me a bias range of -33VDC to -60VDC. I am going to do something similar with this Nomad 100 here in the next few days. You could do something similar to get your control grid bias voltage down in the -20's if you want to try some 6V6's.

I might try a Resonance control on it as well. But first, I am getting ready to try and add a 1/4" jack on the back so I can switch the EQ on & off by a footswitch. Bummer for me, the guy I bought this from did not have the proper Nomad 100 6 button footswitch. He had the 5 button that does not have the EQ switch.

Oh yeah, so far this amp is very sweet with my 2X12 G12-65 cab . . .

re: JJ's
The JJ's are the only one's I am going to try too because of plate voltage level tolerance (450V spec). My thinking is that since JJ's in particular are more like a low power 6L6, and 6L6's actually sound ok with this amp, that they would bring a little more vintage dynamics to Ch1 and Ch2, and possibly thicken up Ch3.

re: Bias
The bias switch on EL34 is -39Vb and on 6L6 is -50Vb. That's a good enough range for most tubes from those families if they are properly "selected" by the tube vendor given Vp and Vb, but may not be enough for the JJ 6v6's. I know the JJ's are a 14W 6v6, so the typical dissipation calculation needs to be amended from the standard 12W 6v6.

Settings:
I'm interested in knowing your settings for Ch3...I haven't had the greatest luck dialing in that channel, its a little too much gain for me and, yes, too bright. Not too bright with my neck pickup, or with the tone rolled back, just too bright with bridge and tone and vol on 10.

EQ Switch.

FYI, when I bought mine (NOS) the store supplied a 5 button switch, and I knew it wasn't the right one when they brought it out from the back, so they had Mesa replace it with the correct one. You never know what Mesa customer service may do for you.

Assuming you are left with having to add a single button, I would wire the extra 1/4" jack into the side of the existing footswitch and tap into the unused midi wire already going to your amp. If there's a spot, maybe just drill a new pushbutton on the existing pedalswitch board, or better yet, repurpose the existing reverb switch, and add a small toggle somewhere on the footswitch for the reverb. (Assuming you use that switch as much as I do....never)

I thought about adding a jack on the footswitch like you suggested. But I figured if i found a 6 button switch to buy, maybe I could sell this 5 button to someone that needs it. So i did not want to hack the footswitch.

I already figured out how to turn the EQ on & off with a simple extra jack on the amp. i was thinking about removing that 4 way channel select rotary knob on the back as i will always be using the footswitch anyway.

I will give you the settings I have right now on my Nomad 100. I am used to dialing in all my various models of Marshall and Fender amps, so these two Mesa amps I got were totally different to dial in for sure. What I found mainly different with the DC-10 and Nomad 100 was the Gain controls need to stay quite low. And yesterday I tried setting the Nomad 100 with the OUTPUT at 10, and then on each channel I brought the Gain up from 0 real slow. AMAZING tones to be had there for sure. Somewhat Plexi'ish for sure. And CH3 still could hold a sustained controlled feedback even with it's gain at 1.

I have not dialed this Nomad in totally as of writing this. My settings are still a ballpark feel at best. And the individual Presence controls, I do not like too much compared to a traditional global Presence circuit tied into the NFB loop. That is a mod I might still tinker with later on. I still need to look into the schematic and see exactly how these three Presence circuits are working, as i am thinking they are just bleeding off certain frequencies to Ground?

Anyway, I still have barely put any time into playing this amp. I am hoping the band is going to get going again back at the rehearsal studio SOON! So, I just stuck all EQ controls at NOON and dialed in a decent tone with my ears and tried not to look at the where the controls were set at physically.

Here are the settings I had from playing the amp earlier this evening. I had the amp cranked up close to live band levels. CH3 has the early Cantrell Dirt era tone just pouring out of it. Think of the song "Junkhead", but the demo version from the Alice In Chains box set that has the heavier mix of the guitars. That is what CH3 is reminding me of. And CH2 is real close to the same voicing but a gain'ed down version. Basically I tried to get CH2 to sound somewhat close to the CH3 voicing. And I wrote down these settings indexing the Nomads potentiometers/knobs to where they would fall if you were looking at a Marshall JCM 800 pots/knobs with the 1 -10, with 5 being NOON or straight up.

CH1: Gain 7 Master 4.5 Pres 5 CLEAN Mode
Treble 5.5 Middle 4 Bass 5

CH2: Gain 3 Master 4 Pres 5 MODERN Mode
Treble 6 Middle 3.5 Bass 2.5

CH3: Gain 3.5 Master 6 Pres 5 MODERN Mode
Treble 5 Middle 5 Bass 3.5

OUTPUT 2.5

I have not messed with the SOLO control yet. And I have noticed that the Reverb sounds quite good, and that is coming from someone that has old Blackface and Silverface Fenders as well as Traynor Custom Reverbs and Ampeg V4's LOL. BUT, the reverb is just a bit weak. But then when you put the channels into the other Modes, the reverb is much loder in the mix. I just had the reverb controls set to aprox. 6. I had the EQ set to a slight smile. But for now I am trying to get the amp to sound good without using the Graphic EQ. Then I can dial in the EQ for taste, or set it up as either a MID boost or a scooped tone option.

This Nomad 100 has Mesa 12AX7-A Russian 1's in all slots except V3 which has a Mesa Chinese 2. And it has two Mesa 6L6 STR 430's in the outer V6, V9 and two Mesa 6L6 STR 420's in the inner V7, V8. And the amp is biased a bit cold running at about 25mA with 470 on the plates. I am going to put an adjustable bias circuit later on as well.

EDIT: I should add that I was playing my homemade SuperStrat with a hot humbucker in the bridge position. Speaker cab was my Marshall 1936 2X12 with G12-65's. Guitar straight to amp. My settings sound great with the single colis as well. CH2 has a sweet Hendrix vibe using the neck PUP. And CH3 has a singing lead tone, but still has a night crisp attack with excellent crunch.

Thanks....I run my gains at about 6, 4, and 2.5.

I've never tried dialing in with a NMV approach, great idea.

And yes, the presence controls are bleed offs to ground in the preamp.

(One other thing....the circuit descriptions I gave above are incorrect. I looked at these schematics about six months ago when the Nomad mod threads were hot, and what I wrote above were the mod's I was going to do to the existing circuit, not how the circuit exists stock....ooopppsssey.)

Ch2 is taken from Ch2 of the Mesa Formula Pre, itself a derivative from heartbreaker Ch2 High, but a little more high mid focussed. Ch3 is similar to one of the rectifier gain channels except with one less gain stage and different tube bias levels.

One other thing.....I put a pair of JJ 6v6 tubes in my Nomad this morning, and they worked awesomelike with the EL34 bias setting. I had them selected by thetubestore for Mesa fixed bias amps, and if anyone wishes to try this, they will set you up. 6v6's are my favorite tube type by far. They make everything better....cleans, crunch and gain. They once again prove that Ch1 of this amp is second to none.

Man Oh Man, I sea I had sum spelling issues last nite on my posts.

:mrgreen:

Hey Tommy, what model Nomad do you have? And have you measured the plate voltage on the 6V6's running in your Nomad?

I just checked the data sheet on the JJ 6V6's and they are rated 500V on the plates which is awesome. But only 450V on the screens. So running them in the EL34 mode with the 1K screen resistors should be a bit safer.

I have a quad of these stashed away here that I will have to tinker with later on.

I have the 100 head, as well. Based on the tones I'm after and how I use this amp, the 55 would have been a better choice for me.

From the schematic, the Plate V are 450, but I've never bothered to confirm with my meter. The JJ's I'm running had an idle current of 23 mA at 400Vp and -36Vb test conditions.

Yep, running on the EL34 setting (-39Vb). Sounds like 6v6 tone to me! FAAAT with thick creamy crunch if you want it. Sit on that open back 1x12 and soak in the tone.

Did I mention that Ch1 is just incredible on this amp? If Mesa had made this channel the only channel on the amp (and not put that bass cut in the NFB), the amp would have been a classic rather than the "RHSC" amp. With the gain around 1:30 to 2:00 I can pretty much go from perfectly clean to full out rock tones just with picking, and sweet but solid tone.

The one thing there is to learn about JJ 6v6's is that they are not 12W like the rest. They have a spec rating of 14W. But they are actually most likely 16-18W tubes. These suckers need biased superhot if you're using spec data (like to 95%). Check out Billm's comments about this tube on his forum dealing with modding Fender Blues Juniors.

What does RHSC stand for?

RHSC=red headed step child :lol:

As far as I know, this amp was voiced to a Santana spec, and Santana plays with his guitar volume and/or tone control rolled back a bit.

The lead channels thicken up to where they're supposed to be as long as you don't have your guitar controls dimed. There's a sweet spot to be found there, too. I run with either volume or tone at about 8.5/10, but everyone has a different guitar. I have a Yammy SBG, so I'm like Santana's RHSC, teehee!

BTW - if your reverb sounds awesome, your amp has been modded....

Well, the reverb on this Nomad has decent sound quality but is quite weak in output.

Would you know what I should check to see if there was a mod done to it? As in, is there a common mod that people are doing to this reverb circuit?

RickyLee said:

Well, the reverb on this Nomad has decent sound quality but is quite weak in output.

Would you know what I should check to see if there was a mod done to it? As in, is there a common mod that people are doing to this reverb circuit?

Click to expand...

The "Nomad Mod's - a visual reference" thread (or some such name) that is probably bumped down to page two of this Modern Amps forum will show and discuss it, if not, one of the 3 threads dedicated to discussing Nomad mods should produce something.

If I recall correctly, one of the mods was to double the number of diodes (eg. add another one in series to each side) in the protection part of the circuit, as there was some belief that the protection diodes were clipping at normal levels. I think there may have also been a change in the feedback resistor of the reverb recovery op amp to increase the gain, as well. I'm not an electronics guru by any means, but my gut instinct would be to increase the resistance the signal sees going into the protection circuit and change the feedback resistor in the recovery stage. However, my major objection to the reverb is not the strength as I run minimal reverb, but its tone. It sounds to me like the signal is passing through a notch boost filter 500 Hz range and basically reproduces some narrow lower frequency metallic type tones that could be mistaken for reverb. I haven't looked into it, but if there's a filtering circuit along the reverb signal path, I'd be finding a better set of values from other manufacturer's designs.

As a side note, get those JJ 6v6's into that amp and biased ASAP. They work extremely well with this amp. I'm using a single pair and they kick the s**t out of the stock 6L6's for tone...(not volume, but who wants/needs 100W anyway?)

Can you post the transconductance numbers they gave you on those JJ 6V6's? I have some stashed away here that I might try. Or I guess I could purchase a quad from where you got yours. I need new valves for this amp anyway. I was considering a quad of Wing C 6L6's but since they raised there prices, I have been reluctant. Even more so when you can buy a quad of JJ 6L6GC's for half the price. I am considering trying some other valves I have stashed away in this Nomad as well - like some Wing C EL34's, JJ KT77's, NOS KT66's, JJ 6CA7's, and maybe even trying a pair of JJ KT88's at half power. KT88's and KT66's are probably my favorites.

Also, I am curious as you say you are only running TWO 6V6's instead of FOUR? What are you doing on the amp's impedance setting in relation to the speaker load?

Have you checked the heater voltages as well? I know that my heaters went up quite a bit when I ran my amp with only two of the four 6L6's. I probably will not be able to get away with only two 6V6's as my MAINS voltage here at my house and where I live runs 123VAC to 125VAC.

The test bed specs for my specific set of tubes were (Vp, Vs) = 400V, Vb=-36V, Idle current was 23mA. I don't think this vendor does a transconductance measurement specifically around this operating point.

I haven't checked heater voltage. According to my tube vendor, the JJ's are virtually indestructable, and I was strongly encouraged to put aside my concerns and just put them in.

As far as speaker load, i'm running an 8 ohm speaker from the 4 ohm jack, but with a single pair of 6v6's and the 4x6L6 transformer, I should be running a 16 ohm speaker from the 4 ohm jack. unfortunately, my only 16 ohm speaker cab is my 4x12. This said, one level of mismatch usually works ok, and these tubes probably have an output impedance more like a 6L6 than a typical 6v6, but this is speculation...these tubes are often described in look and tone as mini-6L6's.

I put them about half way between a 6L6 and a 6v6 in tone, or about 2/3 6L6, 1/3 EL34, which is where this amp needs to be, IMO.

I only run a single pair, because in truth that's more than plenty for home, and just barely enough for gigging.

I ran the Winged C 6L6's in this amp for about 4 years till I dropped one of the tubes on the carpet (from about 3 feet) and it bust like a light bulb. The glass is really thin on that tube. The Winged C had a really solid low end when works well with the Nomad, but I've found that the high end of the Winged C's is so detailed up to dog ear frequencies that it crosses the line into harsh. Mind you, my pair were pretty **** hot tubes.

I am looking at the Nomad 100 schematic, the power supplies section. More precisely, the dropping resistors across the choke as well as the gang of series resistors after the choke that are feeding B+ C circuit. I am curious if these amps actually have all of these resistors, or is it just one resistor with the value of all those that are shown in series?

Why would they put 5 resistors in series, instead of just using one bigger wattage of that total value?

When I was looking at the PCB, I did not notice that many possible B+ dropping resistors. Have you looked into this Tommy? I am thinking about taking a look here this afternoon myself.