NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

[Red_Label]

I was so impressed with the Ceriatone RP 18/36 head that I picked-up a month or so ago that I sold my H&K Grandmeister (AWESOME amp by the way) and picked-up a nice, used Ceriatone JTM45 off of ebay. Just got it last night and only had an hour or two to spend with it. Jury's still out. I need to tweak some more and may need to do some tube swapping, bias adjustments, and/or swap a few components. Clean tones are jangly and hairy with the Strat, and I really dig that. But when I dial-up the gain (whether from the amp itself or a pedal) she gets muddier, fartier and flubbier than I'd prefer. The the 4xEL84-loaded RP 18/36 is much tighter on the bottom and the gain sounds smoother and more refined. My Les Paul Standard just ROARS (like an old school Marshall) through the RP. Whereas the JTM totally prefers my Strat. But I wouldn't say that it's got the Marshall roar or crunch in there anywhere (yet).

Another thing, the JTM is [sort of] loud when running the volumes up, but it's not LOUD. Whereas the RP is LOUD!!! No comparison. Gotta be something not right with the tubes. Going to grab some 6L6s from my local shop tomorrow (they don't have KT66s) and also grab some of my spare 12AX7s and swap-out all of the tubes and see what I end-up. I've heard glowing praises of this amp, and I do like a clean, articulate amp. But I cannot abide a flubby, farty, mushy bottom end. I don't play metal, but I have to have things TIGHT. Will give a further review of this amp once I've seen what I can do to clean that up.

Pic of the "Cherry Twins" on top of my V30/H30-loaded Line 6 4x12. I've got another V30-loaded Line 6 4x12 on the way for a full stereo setup... (Btw... I've owned a lot of nice 4X12s and I would say that the only 4X12 cab that I've ever liked any better than the V30 Line 6 cab is the Bogner straight Uberkab. That cab had some special mojo in there.

 

[zzmoore]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

They have LOTS of satisfied customers with that head...but everybody has different hands, ears, guitars, and speakers.
In its stock form that amp has a Huge bypass cap on V1.....200-250 mics, something like that. A lot of people think that a BF/SF Fender with a 25 Mic cap is too big. You may be able to de-flub it there.....same with the 0.10uF caps after the phase inverter...you could try cutting those in half...or more.
V1 is biased pretty hot with am 820 Ohm Cat resistor. You could try something like the "standard" 1k2-1k5....see if that is more/less to your liking.
Maybe try the AT7 in the phase inverter.
All of that one at a time of course...and after you feel like you have your tubes sorted out.
nice amp.....good luck

 

[Gone_Shootin]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

If you want a tighter bottom end, you're probably going to have to go with EL34s. New Sensor Svetlanas are about the tightest ones out there. They took my Mesa Recto from being an annoyingly flubby amp to being fairly tight. I don't know if your amp can run EL34s without mods, but it might be worth it.

ETA: If you get a chance to try one, you might like a Splawn cab. I have one with a pair of Governors and a pair of Man O Wars, and it sounds better than any cab I've owned.

 

[Red_Label]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

Awesome tips guys! Thanks for those! Will try them as I go thru this "journey".

I don't believe that I can pop EL34s in there without changing out some resistors and such. I'll have to look into that.


I did swap the Gold Lion KT66s for some new JJ 6L6GCs tonight and then biased for 35mv. The cleans were chimey before but really got there with the change. Sounds like my old blackfaces! Which of course was Jim Marshall's goal when he copied them to create the JTM. Only had a chance to play my Strat tonight. I suspect that she's still way too flubby for proper Les Paul rocking ala Def Leppard, ACDC, The Darkness, Thin Lizzy, etc. But the two hours of Dave Gilmour stuff I played thru tonight sounded great! Volume seemed better tonight as well. Will try the LP tomorrow and see if any change there. I did jumper the inputs last night and was not impressed. Mushy mud... not cranked plexi crunch heaven. Maybe I'll see improved results when I try it tomorrow. Did max out the master volume (this amp has a PPIMV) and leave it that way. Supposedly takes the MV out of the circuit. Just ran into the bottom left channel input and ran that volume about "3". Great cleans! Need to find my crunch/roar!

 

[TwilightOdyssey]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

Congrats, hope you get it sorted!

 

[DankStar]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

Interesting. I want a yeti.

 

[Red_Label]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

Interesting. I want a yeti.

Me too!!! I was watching one on Ebay a few weeks ago and REALLY wanted to pull the trigger. But I didn't quite have the funds put together yet when the guy ended the auction early. Reminds me of a Freidman BE... which has got me GASing BAD. Just way too much money though!

 

[Lake Placid Blues]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

The loose bottom comes from the following:

Low filtering
Tube rectifier
Shared Cathode (on V1)
Big cathode caps (on both V1 and V2)
Slope resistor value
KT-66 tubes, which have huge bottom.
The amount of negative feedback.

All of these things can be addressed wholey or in part. You can replace the tube rectifier with a plug in solid state rectifier (you will have to re-bias). There are various grades of how tight a rectifier tube will be too. Mesa GZ-34s seem to be selected to have very little sag.

Changing the low filtering not as easy, but changing or having changed the filter cap cans to higher value cans is feasable. I would only do this if other mods don't do the trick, though.

However, most of the cap values and signal path routing mods are fairly easy. Just find a good lay out picture or diagram of a 68 or 69, 50 watt plexi and change them over. EVH's 67 plexi reportdly had the big cathode caps and possibly the shared cathode so if your going for more of that or a Super Bass response (Doyle Bramhall II, Duane Almann) you might want to keep some of that or make small changes as you go. I think you want a split cathode set up, though, based on your posts.

The negative feedback wire should probably be changed to 8 ohm lug for a tighter response with more gain.


(before working on the amp clip a jumper wire from between the V1 plate resistor and the tube socket to ground; to safely and slowly drain the filter caps through the resistor to ground)

 

[JeffB]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

ube rectified like an actual JTM45?

If so, what you are describing is pretty spot on. Compared to later SS rectified amps, they are flubby/tubby.

That sqid, I think V30s are a really bad match for a JTM45 style amp in general. While tight, they are overkill in the entire midrange for that amp. You should try some alnicos, g12m, or G12h/55hz, something that will let the amp open up, and not make it constipated.

Of course quality tubes/bias is crucial too.

 

[Gone_Shootin]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

The loose bottom comes from the following:

Low filtering
Tube rectifier
Shared Cathode (on V1)
Big cathode caps (on both V1 and V2)
Slope resistor value
KT-66 tubes, which have huge bottom.
The amount of negative feedback.

All of these things can be addressed wholey or in part. You can replace the tube rectifier with a plug in solid state rectifier (you will have to re-bias). There are various grades of how tight a rectifier tube will be too. Mesa GZ-34s seem to be selected to have very little sag.

Changing the low filtering not as easy, but changing or having changed the filter cap cans to higher value cans is feasable. I would only do this if other mods don't do the trick, though.

However, most of the cap values and signal path routing mods are fairly easy. Just find a good lay out picture or diagram of a 68 or 69, 50 watt plexi and change them over. EVH's 67 plexi reportdly had the big cathode caps and possibly the shared cathode so if your going for more of that or a Super Bass response (Doyle Bramhall II, Duane Almann) you might want to keep some of that or make small changes as you go. I think you want a split cathode set up, though, based on your posts.

The negative feedback wire should probably be changed to 8 ohm lug for a tighter response with more gain.


(before working on the amp clip a jumper wire from between the V1 plate resistor and the tube socket to ground; to safely and slowly drain the filter caps through the resistor to ground)

I forgot about the GZ34s. I threw Sovtek 5AR4s (same thing) in my Recto. They helped too.

 

[Gone_Shootin]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

Found this over on the Marshall Forum.

http://www.marshallforum.com/workbench/36042-el34-kt66-interchangeable-jtm45-clone.html

 

[Red_Label]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

Wow... you guys are awesome. I feel like I'm trying to drink from a fire hose here!!!

I've got a very good local amp tech here. I think I'll work with him on this project and look into your advice. I can swap tubes and bias just fine. But am not experienced doing component swaps. I Granted, the P2P turret wiring in this amp really simplifies things (which is why I bought it).

 

[Red_Label]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

As a JTM45 owner (I've modded it twice; once from ass-tone stock, another time was EVH influenced), JTM45s usually have their neg feedback wire (typically purple colored in Marshall-land) on the 16ohm tap. This is a whole metric buttload
of negative feedback and hence a very very clean tone.

Follow Lake Placid Blues's advice: you can easily copy key parts of a Superlead preamp circuit to your own amp to juice the gain and/or remove the flub.

Also, if you switch to EL34/6CA7s, you will need to make a few changes in the power section.

But really, if you have a PTP board this should be a cinch for you or your tech. The question is "which components do I want to change out and what values do I want in there?". This can be done only by trial and experimentation. But again, if you want a quick template to use, try copying parts of the Superlead circuit (a la LPB's advice).

Thanks man. I'm going to forward a link to this thread to my tech and discuss exactly what I want with him, and have him go through your suggestions and chat about it. In case I haven't exactly been clear, what I'm looking for is a perfect blend between Pink Floyd (pretty much already there) and old school ACDC and Def Leppard. I've had awesome luck with my Carl Martin Plexitone OD pedal giving me those tones from semi-clean amps thus far, but in the case of this amp it's just way too flubby and out-of-control sounding (not smooth). Sounds like from what I've read that I'm looking for a JMP style circuit for that sort of thing. So if he can take this JTM and make it half blackface, half JMP I think I'll be in heaven.

Also, I think that I'm going to have him just take the PPIMV out of the circuit and put the lamp back in that spot (where it should be). I use my Plexitone to get my serious OD and lead tones, I've never cared for most amps full OD and usually find all of them flubby (not tight) to a point without hitting the front end with my Plexitone or OCD. So I have no need for the MV. The simpler/cleaner the circuit, the better for me. I'm goin' old school here! (Without the ear-bleeding.)

 

[Gone_Shootin]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

Thanks man. I'm going to forward a link to this thread to my tech and discuss exactly what I want with him, and have him go through your suggestions and chat about it. In case I haven't exactly been clear, what I'm looking for is a perfect blend between Pink Floyd (pretty much already there) and old school ACDC and Def Leppard. I've had awesome luck with my Carl Martin Plexitone OD pedal giving me those tones from semi-clean amps thus far, but in the case of this amp it's just way too flubby and out-of-control sounding (not smooth). Sounds like from what I've read that I'm looking for a JMP style circuit for that sort of thing. So if he can take this JTM and make it half blackface, half JMP I think I'll be in heaven.

Also, I think that I'm going to have him just take the PPIMV out of the circuit and put the lamp back in that spot (where it should be). I use my Plexitone to get my serious OD and lead tones, I've never cared for most amps full OD and usually find all of them flubby (not tight) to a point without hitting the front end with my Plexitone or OCD. So I have no need for the MV. The simpler/cleaner the circuit, the better for me. I'm goin' old school here! (Without the ear-bleeding.)

In that case, you might like the Tung-Sol Reissue EL34s. The engineers played around with the specs a little and managed to come up with an EL34 that has a hint of 6L6 flavor to it.

 

[scorch]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

Remember, a JTM 45 was originally a bass amp ('59 Bassman). It flubs naturally with guitar. Turn down the bass. Or turn it off completely.

I don't know how Ceriatone builds their preamps but you can get rid of a lot of flub in the first gain stage.

 

[zzmoore]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

Remember, a JTM 45 was originally a bass amp ('59 Bassman). It flubs naturally with guitar. Turn down the bass. Or turn it off completely.

I don't know how Ceriatone builds their preamps but you can get rid of a lot of flub in the first gain stage.

This made me laugh.....only because it is so true.
Players tend to Eq amps with their eyes. Lots of "classic" era Marshall guys run the Bass at Zero. How DO you have the knobs set.?

But let me ask the OP...because I may have misunderstood...are you saying the amp cannot keep up with the bass demands of your playing, and sags in the low end.?
Or are you saying there is too much bass and the speakers fart and flub because of so much bass response.?

Sagging low end would/could certainly benefit from a SS Rectifier, and maybe 2x the first filter (as a few members have already advised).

But if you cannot get rid of enough bass, those steps would be the last thing you want to do...killing capacitance in the preamp and PI would be a better call.

Whichever avenue you choose...it can be a big help to use jumper wires and not solder things right away. The NFB would be an easy example. Desolder it from the Z Selector...and use a jumper wire to easily go between (for example) the 8 and 16 Ohm tap...so you can really Hear/Feel the difference between the 2. Do it a few times to be sure... IME most guitar amps supply plenty of bass for your typical Blues, Rock, Country, Blues-Rock...but maybe not for detuned, chug chug, harder, metal stuff that I am not familiar with.

Try to implement that technique as you co through your JTM. Pick one procedure at a time...use jumper wires...go back and forth a few times so you can see if something is really an improvement or not.
best

 

[Red_Label]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

This is a familiar Edward tune I did with my modded JTM45 (+ EP3 preamp, + MXR 6 Band EQ) where the guitar is tuned down 1/2 step, plus the low E is detuned to D. The tone is not flubby in the least and the filtering and rectifier are stock JTM45 spec:

http://soundclick.com/share.cfm?id=12349401

Great clip man! You definitely captured the sag and variac-starved feel of Ed's tone there. That's awesome to hear that those tones can be found in the JTM (when configured correctly).

 

[Red_Label]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

*** UPDATE ***

Firstly, thanks for the additional advice guys. When I started this thread, I had NO idea that I'd receive such detailed, knowledgeable replies. I figured that I'd have to ask my question on the Marshall or Metro forums. SD Forum delivers!

And now for the update... today was the day that I planned to pick up my 2001 Gibson LP Standard and tweak with the amp since I'd swapped-out the power tubes to 6L6GCs and rebiased. First, I plugged-into the upper, left-hand input and jumpered from the bottom left to the top right input. This was the suggestion of the private ebay seller that I bought the amp from. So I played around with the channel volumes, master volume, and tone controls to see if I could get some sort of old school Marshall crunch. Nope... still pretty muddy, mushy, and just not the quality crunch or roar that I was expecting or hoping for. To be fair, I found my JCM800 2203X to be a bit soft as well without my OCD in front of it. I've found that to be the case with most of the best tube amps that I've owned. I just find that most amp distortion isn't tight enough for me on its own. But the 800 definitely had a better, more-defined roar in un-boosted config than the JTM has thus far.

So I un-jumpered the channels and just plugged back into the lower left-hand input (where I prefer it so far) and then made sure the MV was back to max, therefore taking the MV out of the circuit. I then kicked in the crunch channel of my Plexitone and was rewarded with a "proper" rock tone. After that, it was a matter of tweaking the tone controls on the amp to tighten things up further. As someone mentioned earlier, I rolled back the bass a ways and experimented with the mids, treble, and presence. Right now I find things most pleasing with the presence and treble rolled all the way off. It's a plenty bright amp without any of that on. After that, it's just a matter of playing around with the bass and mids to get the tones I'm looking for. The bass was definitely too much with the KT66s. I think that the tone itself was flubby/farty, but that I was also pushing the speakers too hard and causing them to woof and flub. I deliberately tweaked the tone to avoid that today and was pretty successful in doing that.

I played through a bunch of old school, and newer school rock. The Darkness, Journey, Pat Benetar... to Tool, Creed, and 3 Doors Down (the latter hard-rock stuff done with the hotter channel of the Plexitone on). The amp performed well. Bottom was MUCH tighter. Amp sounded more organic and had more clarity. I think that the 6L6s and rebias really helped a bit. Is it as sweetly crunchy as the RP36 or other great old school Marshall amps? Maybe not. I will likely play with some of your suggestions over time. Would like to try EL34s in there... but it sounds like a bit of a process to do the switch.

Right now I'm putting any more changes on hold until I get my second 4X12 cab later next week. I want to run both my Ceriatones in stereo and see if/how they compliment each other. Over the years I've learned that I get a much bigger tone in stereo setups if there are complimentary differences between the two rigs. I feel like it's worth a shot to see if the two amps make something bigger than the two individual parts. The RP would likely be the stronger for old school rock, the JTM for clean tones and more scoopy, modern hard rock. But together, I would imagine the tone will be BIG. Will give an update on that when the cab comes, as well as future findings and changes in amp configuration.

Thanks again for your input. It's been valuable and will no doubt play a role in future decisions regarding this amp. And for any future lurkers looking at this thread who are researching JTM45s (the Ceriatone in particular)... I do like this amp and it's an amazingly quality piece. I'm still in the tweaking phase to make it suit my style(s) and my ears and hands. I wish I'd saved the gut shots of this that were on ebay, but I deleted that after I received it. At some point, I'll take the chassis out of the headshell and photo it and link it here. It's pretty impressive. I've been inside my past great amps (Bogners, VHT, Engl, etc) and this thing is just so much more beautiful to me (no PCBs and simplicity-defined). I had been watching some reissue plexis on ebay... the JTM and 1987X in particular. But I've seen the gut shots of those amps and they just don't impress me with the PCBs. Yes, they are simple and duplicate the same circuit. But I'm just at a point in my life where I'm really going backward in time with all of my music gear. I've been dumping new tech in guitars and amps and going back to old P2P plexi type amps and Fender Strats and Gibson Les Pauls. I'm becoming a tone purist and am just not digging newer, higher-tech stuff these days. I don't like compression, saturation, or other things that take away from the clean purity of the guitar and amp (to a reasonable extent of course -- or I'd just go back to playing acoustic... LOL).

 

[Stratman]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

If you have a JTM-45, then the old school trick is to just jump your channels.

Treble channel set higher than the normal channel.

 

[Gone_Shootin]

Re: NAD: Ceriatone JTM45 (2xKT66, 50-watter)...

I hear ya on having different sounding amps in a stereo rig, Red Label. Right now, one of my favorite things is to run my Recto and Splawn together. They compliment each other so well.